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Keywords: lwapp, capwap
Independent Submission P. Calhoun
Request for Comments: 5412 R. Suri
Category: Historic N. Cam-Winget
ISSN: 2070-1721 Cisco Systems, Inc.
M. Williams
GWhiz Arts & Sciences
S. Hares
B. O'Hara
S.Kelly
February 2010
Lightweight Access Point Protocol
Abstract
In recent years, there has been a shift in wireless LAN (WLAN)
product architectures from autonomous access points to centralized
control of lightweight access points. The general goal has been to
move most of the traditional wireless functionality such as access
control (user authentication and authorization), mobility, and radio
management out of the access point into a centralized controller.
The IETF's CAPWAP (Control and Provisioning of Wireless Access
Points) WG has identified that a standards-based protocol is
necessary between a wireless Access Controller and Wireless
Termination Points (the latter are also commonly referred to as
Lightweight Access Points). This specification defines the
Lightweight Access Point Protocol (LWAPP), which addresses the
CAPWAP's (Control and Provisioning of Wireless Access Points)
protocol requirements. Although the LWAPP protocol is designed to be
flexible enough to be used for a variety of wireless technologies,
this specific document describes the base protocol and an extension
that allows it to be used with the IEEE's 802.11 wireless LAN
protocol.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for the historical record.
This document defines a Historic Document for the Internet community.
This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Calhoun, et al. Historic [Page 1]
RFC 5412 Lightweight Access Point Protocol February 2010
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5412.
IESG Note
This RFC documents the LWAPP protocol as it was when submitted to the
IETF as a basis for further work in the CAPWAP Working Group, and
therefore it may resemble the CAPWAP protocol specification in RFC
5415 as well as other IETF work. This RFC is being published solely
for the historical record. The protocol described in this RFC has
not been thoroughly reviewed and may contain errors and omissions.
RFC 5415 documents the standards track solution for the CAPWAP
Working Group and obsoletes any and all mechanisms defined in this
RFC. This RFC is not a candidate for any level of Internet Standard
and should not be used as a basis for any sort of Internet
deployment.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Calhoun, et al. Historic [Page 2]
RFC 5412 Lightweight Access Point Protocol February 2010
Table of Contents
1. Introduction ....................................................8
1.1. Conventions Used in This Document ..........................9
2. Protocol Overview ..............................................10
2.1. Wireless Binding Definition ...............................11
2.2. LWAPP State Machine Definition ............................12
3. LWAPP Transport Layers .........................................20
3.1. LWAPP Transport Header ....................................21
3.1.1. VER Field ..........................................21
3.1.2. RID Field ..........................................21
3.1.3. C Bit ..............................................21
3.1.4. F Bit ..............................................21
3.1.5. L Bit ..............................................22
3.1.6. Fragment ID ........................................22
3.1.7. Length .............................................22
3.1.8. Status and WLANS ...................................22
3.1.9. Payload ............................................22
3.2. Using IEEE 802.3 MAC as LWAPP Transport ...................22
3.2.1. Framing ............................................23
3.2.2. AC Discovery .......................................23
3.2.3. LWAPP Message Header Format over IEEE 802.3
MAC Transport ......................................23
3.2.4. Fragmentation/Reassembly ...........................24
3.2.5. Multiplexing .......................................24
3.3. Using IP/UDP as LWAPP Transport ...........................24
3.3.1. Framing ............................................24
3.3.2. AC Discovery .......................................25
3.3.3. LWAPP Message Header Format over IP/UDP Transport ..25
3.3.4. Fragmentation/Reassembly for IPv4 ..................26
3.3.5. Fragmentation/Reassembly for IPv6 ..................26
3.3.6. Multiplexing .......................................26
4. LWAPP Packet Definitions .......................................26
4.1. LWAPP Data Messages .......................................27
4.2. LWAPP Control Messages Overview ...........................27
4.2.1. Control Message Format .............................28
4.2.2. Message Element Format .............................29
4.2.3. Quality of Service .................................31
5. LWAPP Discovery Operations .....................................31
5.1. Discovery Request .........................................31
5.1.1. Discovery Type .....................................32
5.1.2. WTP Descriptor .....................................33
5.1.3. WTP Radio Information ..............................34
5.2. Discovery Response ........................................34
5.2.1. AC Address .........................................35
5.2.2. AC Descriptor ......................................35
5.2.3. AC Name ............................................36
5.2.4. WTP Manager Control IPv4 Address ...................37
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RFC 5412 Lightweight Access Point Protocol February 2010
5.2.5. WTP Manager Control IPv6 Address ...................37
5.3. Primary Discovery Request .................................38
5.3.1. Discovery Type .....................................38
5.3.2. WTP Descriptor .....................................38
5.3.3. WTP Radio Information ..............................38
5.4. Primary Discovery Response ................................38
5.4.1. AC Descriptor ......................................39
5.4.2. AC Name ............................................39
5.4.3. WTP Manager Control IPv4 Address ...................39
5.4.4. WTP Manager Control IPv6 Address ...................39
6. Control Channel Management .....................................39
6.1. Join Request ..............................................39
6.1.1. WTP Descriptor .....................................40
6.1.2. AC Address .........................................40
6.1.3. WTP Name ...........................................40
6.1.4. Location Data ......................................41
6.1.5. WTP Radio Information ..............................41
6.1.6. Certificate ........................................41
6.1.7. Session ID .........................................42
6.1.8. Test ...............................................42
6.1.9. XNonce .............................................42
6.2. Join Response .............................................43
6.2.1. Result Code ........................................44
6.2.2. Status .............................................44
6.2.3. Certificate ........................................45
6.2.4. WTP Manager Data IPv4 Address ......................45
6.2.5. WTP Manager Data IPv6 Address ......................45
6.2.6. AC IPv4 List .......................................46
6.2.7. AC IPv6 List .......................................46
6.2.8. ANonce .............................................47
6.2.9. PSK-MIC ............................................48
6.3. Join ACK ..................................................48
6.3.1. Session ID .........................................49
6.3.2. WNonce .............................................49
6.3.3. PSK-MIC ............................................49
6.4. Join Confirm ..............................................49
6.4.1. Session ID .........................................50
6.4.2. PSK-MIC ............................................50
6.5. Echo Request ..............................................50
6.6. Echo Response .............................................50
6.7. Key Update Request ........................................51
6.7.1. Session ID .........................................51
6.7.2. XNonce .............................................51
6.8. Key Update Response .......................................51
6.8.1. Session ID .........................................51
6.8.2. ANonce .............................................51
6.8.3. PSK-MIC ............................................52
6.9. Key Update ACK ............................................52
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6.9.1. WNonce .............................................52
6.9.2. PSK-MIC ............................................52
6.10. Key Update Confirm .......................................52
6.10.1. PSK-MIC ...........................................52
6.11. Key Update Trigger .......................................52
6.11.1. Session ID ........................................53
7. WTP Configuration Management ...................................53
7.1. Configuration Consistency .................................53
7.2. Configure Request .........................................54
7.2.1. Administrative State ...............................54
7.2.2. AC Name ............................................55
7.2.3. AC Name with Index .................................55
7.2.4. WTP Board Data .....................................56
7.2.5. Statistics Timer ...................................56
7.2.6. WTP Static IP Address Information ..................57
7.2.7. WTP Reboot Statistics ..............................58
7.3. Configure Response ........................................58
7.3.1. Decryption Error Report Period .....................59
7.3.2. Change State Event .................................59
7.3.3. LWAPP Timers .......................................60
7.3.4. AC IPv4 List .......................................60
7.3.5. AC IPv6 List .......................................61
7.3.6. WTP Fallback .......................................61
7.3.7. Idle Timeout .......................................61
7.4. Configuration Update Request ..............................62
7.4.1. WTP Name ...........................................62
7.4.2. Change State Event .................................62
7.4.3. Administrative State ...............................62
7.4.4. Statistics Timer ...................................62
7.4.5. Location Data ......................................62
7.4.6. Decryption Error Report Period .....................62
7.4.7. AC IPv4 List .......................................62
7.4.8. AC IPv6 List .......................................62
7.4.9. Add Blacklist Entry ................................63
7.4.10. Delete Blacklist Entry ............................63
7.4.11. Add Static Blacklist Entry ........................64
7.4.12. Delete Static Blacklist Entry .....................64
7.4.13. LWAPP Timers ......................................65
7.4.14. AC Name with Index ................................65
7.4.15. WTP Fallback ......................................65
7.4.16. Idle Timeout ......................................65
7.5. Configuration Update Response .............................65
7.5.1. Result Code ........................................65
7.6. Change State Event Request ................................65
7.6.1. Change State Event .................................66
7.7. Change State Event Response ...............................66
7.8. Clear Config Indication ...................................66
8. Device Management Operations ...................................66
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8.1. Image Data Request ........................................66
8.1.1. Image Download .....................................67
8.1.2. Image Data .........................................67
8.2. Image Data Response .......................................68
8.3. Reset Request .............................................68
8.4. Reset Response ............................................68
8.5. WTP Event Request .........................................68
8.5.1. Decryption Error Report ............................69
8.5.2. Duplicate IPv4 Address .............................69
8.5.3. Duplicate IPv6 Address .............................70
8.6. WTP Event Response ........................................70
8.7. Data Transfer Request .....................................71
8.7.1. Data Transfer Mode .................................71
8.7.2. Data Transfer Data .................................71
8.8. Data Transfer Response ....................................72
9. Mobile Session Management ......................................72
9.1. Mobile Config Request .....................................72
9.1.1. Delete Mobile ......................................73
9.2. Mobile Config Response ....................................73
9.2.1. Result Code ........................................74
10. LWAPP Security ................................................74
10.1. Securing WTP-AC Communications ...........................74
10.2. LWAPP Frame Encryption ...................................75
10.3. Authenticated Key Exchange ...............................76
10.3.1. Terminology .......................................76
10.3.2. Initial Key Generation ............................77
10.3.3. Refreshing Cryptographic Keys .....................81
10.4. Certificate Usage ........................................82
11. IEEE 802.11 Binding ...........................................82
11.1. Division of Labor ........................................82
11.1.1. Split MAC .........................................83
11.1.2. Local MAC .........................................85
11.2. Roaming Behavior and 802.11 Security .....................87
11.3. Transport-Specific Bindings ..............................88
11.3.1. Status and WLANS Field ............................88
11.4. BSSID to WLAN ID Mapping .................................89
11.5. Quality of Service .......................................89
11.6. Data Message Bindings ....................................90
11.7. Control Message Bindings .................................90
11.7.1. Mobile Config Request .............................90
11.7.2. WTP Event Request .................................96
11.8. 802.11 Control Messages ..................................97
11.8.1. IEEE 802.11 WLAN Config Request ...................98
11.8.2. IEEE 802.11 WLAN Config Response .................103
11.8.3. IEEE 802.11 WTP Event ............................103
11.9. Message Element Bindings ................................105
11.9.1. IEEE 802.11 WTP WLAN Radio Configuration .........105
11.9.2. IEEE 802.11 Rate Set .............................107
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RFC 5412 Lightweight Access Point Protocol February 2010
11.9.3. IEEE 802.11 Multi-Domain Capability ..............107
11.9.4. IEEE 802.11 MAC Operation ........................108
11.9.5. IEEE 802.11 Tx Power .............................109
11.9.6. IEEE 802.11 Tx Power Level .......................110
11.9.7. IEEE 802.11 Direct Sequence Control ..............110
11.9.8. IEEE 802.11 OFDM Control .........................111
11.9.9. IEEE 802.11 Antenna ..............................112
11.9.10. IEEE 802.11 Supported Rates .....................113
11.9.11. IEEE 802.11 CFP Status ..........................114
11.9.12. IEEE 802.11 WTP Mode and Type ...................114
11.9.13. IEEE 802.11 Broadcast Probe Mode ................115
11.9.14. IEEE 802.11 WTP Quality of Service ..............115
11.9.15. IEEE 802.11 MIC Error Report From Mobile ........117
11.10. IEEE 802.11 Message Element Values .....................117
12. LWAPP Protocol Timers ........................................118
12.1. MaxDiscoveryInterval ....................................118
12.2. SilentInterval ..........................................118
12.3. NeighborDeadInterval ....................................118
12.4. EchoInterval ............................................118
12.5. DiscoveryInterval .......................................118
12.6. RetransmitInterval ......................................119
12.7. ResponseTimeout .........................................119
12.8. KeyLifetime .............................................119
13. LWAPP Protocol Variables .....................................119
13.1. MaxDiscoveries ..........................................119
13.2. DiscoveryCount ..........................................119
13.3. RetransmitCount .........................................119
13.4. MaxRetransmit ...........................................120
14. NAT Considerations ...........................................120
15. Security Considerations ......................................121
15.1. Certificate-Based Session Key Establishment .............122
15.2. PSK-Based Session Key Establishment .....................123
16. Acknowledgements .............................................123
17. References ...................................................123
17.1. Normative References ....................................123
17.2. Informative References ..................................124
Calhoun, et al. Historic [Page 7]
RFC 5412 Lightweight Access Point Protocol February 2010
1. Introduction
Unlike wired network elements, Wireless Termination Points (WTPs)
require a set of dynamic management and control functions related to
their primary task of connecting the wireless and wired mediums.
Today, protocols for managing WTPs are either manual static
configuration via HTTP, proprietary Layer 2-specific, or non-existent
(if the WTPs are self-contained). The emergence of simple 802.11
WTPs that are managed by a WLAN appliance or switch (also known as an
Access Controller, or AC) suggests that having a standardized,
interoperable protocol could radically simplify the deployment and
management of wireless networks. In many cases, the overall control
and management functions themselves are generic and could apply to an
AP for any wireless Layer 2 (L2) protocol. Being independent of
specific wireless Layer 2 technologies, such a protocol could better
support interoperability between Layer 2 devices and enable smoother
intertechnology handovers.
The details of how these functions would be implemented are dependent
on the particular Layer 2 wireless technology. Such a protocol would
need provisions for binding to specific technologies.
LWAPP assumes a network configuration that consists of multiple WTPs
communicating either via Layer 2 (Medium Access Control (MAC)) or
Layer 3 (IP) to an AC. The WTPs can be considered as remote radio
frequency (RF) interfaces, being controlled by the AC. The AC
forwards all L2 frames it wants to transmit to a WTP via the LWAPP
protocol. Packets from mobile nodes are forwarded by the WTP to the
AC, also via this protocol. Figure 1 illustrates this arrangement as
applied to an IEEE 802.11 binding.
+-+ 802.11 frames +-+
| |--------------------------------| |
| | +-+ | |
| |--------------| |---------------| |
| | 802.11 PHY/ | | LWAPP | |
| | MAC sublayer | | | |
+-+ +-+ +-+
STA WTP AC
Figure 1: LWAPP Architecture
Calhoun, et al. Historic [Page 8]
RFC 5412 Lightweight Access Point Protocol February 2010
Security is another aspect of Wireless Termination Point management
that is not well served by existing solutions. Provisioning WTPs
with security credentials, and managing which WTPs are authorized to
provide service are today handled by proprietary solutions. Allowing
these functions to be performed from a centralized AC in an
interoperable fashion increases manageability and allows network
operators to more tightly control their wireless network
infrastructure.
This document describes the Lightweight Access Point Protocol
(LWAPP), allowing an AC to manage a collection of WTPs. The protocol
is defined to be independent of Layer 2 technology, but an 802.11
binding is provided for use in growing 802.11 wireless LAN networks.
Goals:
The following are goals for this protocol:
1. Centralization of the bridging, forwarding, authentication, and
policy enforcement functions for a wireless network. Optionally,
the AC may also provide centralized encryption of user traffic.
This will permit reduced cost and higher efficiency when applying
the capabilities of network processing silicon to the wireless
network, as it has already been applied to wired LANs.
2. Permit shifting of the higher-level protocol processing burden
away from the WTP. This leaves the computing resource of the WTP
to the timing-critical applications of wireless control and
access. This makes the most efficient use of the computing power
available in WTPs that are the subject of severe cost pressure.
3. Providing a generic encapsulation and transport mechanism, the
protocol may be applied to other access point types in the future
by adding the binding.
The LWAPP protocol concerns itself solely with the interface between
the WTP and the AC. Inter-AC, or mobile-to-AC communication is
strictly outside the scope of this document.
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
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RFC 5412 Lightweight Access Point Protocol February 2010
2. Protocol Overview
LWAPP is a generic protocol defining how Wireless Termination Points
communicate with Access Controllers. Wireless Termination Points and
Access Controllers may communicate either by means of Layer 2
protocols or by means of a routed IP network.
LWAPP messages and procedures defined in this document apply to both
types of transports unless specified otherwise. Transport
independence is achieved by defining formats for both MAC-level and
IP-level transport (see Section 3). Also defined are framing,
fragmentation/reassembly, and multiplexing services to LWAPP for each
transport type.
The LWAPP Transport layer carries two types of payload. LWAPP data
messages are forwarded wireless frames. LWAPP control messages are
management messages exchanged between a WTP and an AC. The LWAPP
transport header defines the "C-bit", which is used to distinguish
data and control traffic. When used over IP, the LWAPP data and
control traffic are also sent over separate UDP ports. Since both
data and control frames can exceed Path Maximum Transmission Unit
(PMTU), the payload of an LWAPP data or control message can be
fragmented. The fragmentation behavior is highly dependent upon the
lower-layer transport and is defined in Section 3.
The Lightweight Access Protocol (LWAPP) begins with a discovery
phase. The WTPs send a Discovery Request frame, causing any Access
Controller (AC), receiving that frame to respond with a Discovery
Response. From the Discovery Responses received, a WTP will select
an AC with which to associate, using the Join Request and Join
Response. The Join Request also provides an MTU discovery mechanism,
to determine whether there is support for the transport of large
frames between the WTP and its AC. If support for large frames is
not present, the LWAPP frames will be fragmented to the maximum
length discovered to be supported by the network.
Once the WTP and the AC have joined, a configuration exchange is
accomplished that will cause both devices to agree on version
information. During this exchange, the WTP may receive provisioning
settings. For the 802.11 binding, this information would typically
include a name (802.11 Service Set Identifier, SSID), and security
parameters, the data rates to be advertised, as well as the radio
channel (channels, if the WTP is capable of operating more than one
802.11 MAC and Physical Layer (PHY) simultaneously) to be used.
Finally, the WTPs are enabled for operation.
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When the WTP and AC have completed the version and provision exchange
and the WTP is enabled, the LWAPP encapsulates the wireless frames
sent between them. LWAPP will fragment its packets, if the size of
the encapsulated wireless user data (Data) or protocol control
(Management) frames cause the resultant LWAPP packet to exceed the
MTU supported between the WTP and AC. Fragmented LWAPP packets are
reassembled to reconstitute the original encapsulated payload.
In addition to the functions thus far described, LWAPP also provides
for the delivery of commands from the AC to the WTP for the
management of devices that are communicating with the WTP. This may
include the creation of local data structures in the WTP for the
managed devices and the collection of statistical information about
the communication between the WTP and the 802.11 devices. LWAPP
provides the ability for the AC to obtain any statistical information
collected by the WTP.
LWAPP also provides for a keepalive feature that preserves the
communication channel between the WTP and AC. If the AC fails to
appear alive, the WTP will try to discover a new AC to communicate
through.
This document uses terminology defined in [5].
2.1. Wireless Binding Definition
This draft standard specifies a protocol independent of a specific
wireless access point radio technology. Elements of the protocol are
designed to accommodate specific needs of each wireless technology in
a standard way. Implementation of this standard for a particular
wireless technology must follow the binding requirements defined for
that technology. This specification includes a binding for the IEEE
802.11 (see Section 11).
When defining a binding for other technologies, the authors MUST
include any necessary definitions for technology-specific messages
and all technology-specific message elements for those messages. At
a minimum, a binding MUST provide the definition for a binding-
specific Statistics message element, which is carried in the WTP
Event Request message, and Add Mobile message element, which is
carried in the Mobile Configure Request. If any technology-specific
message elements are required for any of the existing LWAPP messages
defined in this specification, they MUST also be defined in the
technology-binding document.
The naming of binding-specific message elements MUST begin with the
name of the technology type, e.g., the binding for IEEE 802.11,
provided in this standard, begins with "IEEE 802.11".
Calhoun, et al. Historic [Page 11]
RFC 5412 Lightweight Access Point Protocol February 2010
2.2. LWAPP State Machine Definition
The following state diagram represents the life cycle of a WTP-AC
session:
/-------------\
| v
| +------------+
| C| Idle |<-----------------------------------\
| +------------+<-----------------------\ |
| ^ |a ^ | |
| | | \----\ | |
| | | | +------------+ |
| | | | -------| Key Confirm| |
| | | | w/ +------------+ |
| | | | | ^ |
| | | |t V |5 |
| | | +-----------+ +------------+ |
| / | C| Run | | Key Update | |
| / | r+-----------+------>+------------+ |
| / | ^ |s u x| |
| | v | | | |
| | +--------------+ | | v |y
| | C| Discovery | q| \--------------->+-------+
| | b+--------------+ +-------------+ | Reset |
| | |d f| ^ | Configure |------->+-------+
| | | | | +-------------+p ^
| |e v | | ^ |
| +---------+ v |i 2| |
| C| Sulking | +------------+ +--------------+ |
| +---------+ C| Join |--->| Join-Confirm | |
| g+------------+z +--------------+ |
| |h m| 3| |4 |
| | | | v |o
|\ | | | +------------+
\\-----------------/ \--------+---->| Image Data |C
\------------------------------------/ +------------+n
Figure 2: LWAPP State Machine
The LWAPP state machine, depicted above, is used by both the AC and
the WTP. For every state defined, only certain messages are
permitted to be sent and received. In all of the LWAPP control
messages defined in this document, the state for which each command
is valid is specified.
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RFC 5412 Lightweight Access Point Protocol February 2010
Note that in the state diagram figure above, the 'C' character is
used to represent a condition that causes the state to remain the
same.
The following text discusses the various state transitions, and the
events that cause them.
Idle to Discovery (a): This is the initialization state.
WTP: The WTP enters the Discovery state prior to transmitting the
first Discovery Request (see Section 5.1). Upon entering
this state, the WTP sets the DiscoveryInterval timer (see
Section 12). The WTP resets the DiscoveryCount counter to
zero (0) (see Section 13). The WTP also clears all
information from ACs (e.g., AC Addresses) it may have
received during a previous discovery phase.
AC: The AC does not need to maintain state information for the
WTP upon reception of the Discovery Request, but it MUST
respond with a Discovery Response (see Section 5.2).
Discovery to Discovery (b): This is the state the WTP uses to
determine to which AC it wishes to connect.
WTP: This event occurs when the DiscoveryInterval timer expires.
The WTP transmits a Discovery Request to every AC to which
the WTP hasn't received a response. For every transition to
this event, the WTP increments the DisoveryCount counter.
See Section 5.1 for more information on how the WTP knows to
which ACs it should transmit the Discovery Requests. The
WTP restarts the DiscoveryInterval timer.
AC: This is a noop.
Discovery to Sulking (d): This state occurs on a WTP when Discovery
or connectivity to the AC fails.
WTP: The WTP enters this state when the DiscoveryInterval timer
expires and the DiscoveryCount variable is equal to the
MaxDiscoveries variable (see Section 13). Upon entering
this state, the WTP will start the SilentInterval timer.
While in the Sulking state, all LWAPP messages received are
ignored.
AC: This is a noop.
Sulking to Idle (e): This state occurs on a WTP when it must restart
the discovery phase.
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RFC 5412 Lightweight Access Point Protocol February 2010
WTP: The WTP enters this state when the SilentInterval timer (see
Section 12) expires.
AC: This is a noop.
Discovery to Join (f): This state is used by the WTP to confirm its
commitment to an AC that it wishes to be provided service.
WTP: The WTP selects the best AC based on the information it
gathered during the discovery phase. It then transmits a
Join Request (see Section 6.1) to its preferred AC. The WTP
starts the WaitJoin timer (see Section 12).
AC: The AC enters this state for the given WTP upon reception of
a Join Request. The AC processes the request and responds
with a Join Response.
Join to Join (g): This state transition occurs during the join
phase.
WTP: The WTP enters this state when the WaitJoin timer expires,
and the underlying transport requires LWAPP MTU detection
(Section 3).
AC: This state occurs when the AC receives a retransmission of a
Join Request. The WTP processes the request and responds
with the Join Response.
Join to Idle (h): This state is used when the join process has
failed.
WTP: This state transition occurs if the WTP is configured to use
pre-shared key (PSK) security and receives a Join Response
that includes an invalid PSK-MIC (Message Integrity Check)
message element.
AC: The AC enters this state when it transmits an unsuccessful
Join Response.
Join to Discovery (i): This state is used when the join process has
failed.
WTP: The WTP enters this state when it receives an unsuccessful
Join Response. Upon entering this state, the WTP sets the
DiscoveryInterval timer (see Section 12). The WTP resets
the DiscoveryCount counter to zero (0) (see Section 13).
This state transition may also occur if the PSK-MIC (see
Section 6.2.9) message element is invalid.
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AC: This state transition is invalid.
Join to Join-Confirm (z): This state is used to provide key
confirmation during the join process.
WTP: This state is entered when the WTP receives a Join Response.
In the event that certificate-based security is utilized,
this transition will occur if the Certificate message
element is present and valid in the Join Response. For pre-
shared key security, the Join Response must include a valid
and authenticated PSK-MIC message element. The WTP MUST
respond with a Join ACK, which is used to provide key
confirmation.
AC: The AC enters this state when it receives a valid Join ACK.
For certificate-based security, the Join ACK MUST include
the WNonce message element. For pre-shared key security,
the message must include a valid PSK-MIC message element.
The AC MUST respond with a Join Confirm message, which
includes the Session Key message element.
Join-Confirm to Idle (3): This state is used when the join process
has failed.
WTP: This state transition occurs when the WTP receives an
invalid Join Confirm.
AC: The AC enters this state when it receives an invalid Join
ACK.
Join-Confirm to Configure (2): This state is used by the WTP and the
AC to exchange configuration information.
WTP: The WTP enters this state when it receives a successful Join
Confirm and determines that its version number and the
version number advertised by the AC are the same. The WTP
transmits the Configure Request (see Section 7.2) message to
the AC with a snapshot of its current configuration. The
WTP also starts the ResponseTimeout timer (see Section 12).
AC: This state transition occurs when the AC receives the
Configure Request from the WTP. The AC must transmit a
Configure Response (see Section 7.3) to the WTP, and may
include specific message elements to override the WTP's
configuration.
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Join-Confirm to Image Data (4): This state is used by the WTP and
the AC to download executable firmware.
WTP: The WTP enters this state when it receives a successful Join
Confirm, and determines that its version number and the
version number advertised by the AC are different. The WTP
transmits the Image Data Request (see Section 8.1) message
requesting that the AC's latest firmware be initiated.
AC: This state transition occurs when the AC receives the Image
Data Request from the WTP. The AC must transmit an Image
Data Response (see Section 8.2) to the WTP, which includes a
portion of the firmware.
Image Data to Image Data (n): This state is used by the WTP and the
AC during the firmware download phase.
WTP: The WTP enters this state when it receives an Image Data
Response that indicates that the AC has more data to send.
AC: This state transition occurs when the AC receives the Image
Data Request from the WTP while already in this state, and
it detects that the firmware download has not completed.
Image Data to Reset (o): This state is used when the firmware
download is completed.
WTP: The WTP enters this state when it receives an Image Data
Response that indicates that the AC has no more data to
send, or if the underlying LWAPP transport indicates a link
failure. At this point, the WTP reboots itself.
AC: This state transition occurs when the AC receives the Image
Data Request from the WTP while already in this state, and
it detects that the firmware download has completed or if
the underlying LWAPP transport indicates a link failure.
Note that the AC itself does not reset, but it places the
specific WTP's context it is communicating with in the reset
state: meaning that it clears all state associated with the
WTP.
Configure to Reset (p): This state transition occurs if the
configure phase fails.
WTP: The WTP enters this state when the reliable transport fails
to deliver the Configure Request, or if the ResponseTimeout
timer (see Section 12) expires.
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AC: This state transition occurs if the AC is unable to transmit
the Configure Response to a specific WTP. Note that the AC
itself does not reset, but it places the specific WTP's
context it is communicating with in the reset state: meaning
that it clears all state associated with the WTP.
Configure to Run (q): This state transition occurs when the WTP and
AC enter their normal state of operation.
WTP: The WTP enters this state when it receives a successful
Configure Response from the AC. The WTP initializes the
HeartBeat timer (see Section 12), and transmits the Change
State Event Request message (see Section 7.6).
AC: This state transition occurs when the AC receives the Change
State Event Request (see Section 7.6) from the WTP. The AC
responds with a Change State Event Response (see Section
7.7) message. The AC must start the Session ID and
NeighborDead timers (see Section 12).
Run to Run (r): This is the normal state of operation.
WTP: This is the WTP's normal state of operation, and there are
many events that cause this to occur:
Configuration Update: The WTP receives a Configuration Update
Request (see Section 7.4). The WTP MUST respond with a
Configuration Update Response (see Section 7.5).
Change State Event: The WTP receives a Change State Event
Response, or determines that it must initiate a Change State
Event Request, as a result of a failure or change in the state
of a radio.
Echo Request: The WTP receives an Echo Request message
(Section 6.5), to which it MUST respond with an Echo Response
(see Section 6.6).
Clear Config Indication: The WTP receives a Clear Config
Indication message (Section 7.8). The WTP MUST reset its
configuration back to manufacturer defaults.
WTP Event: The WTP generates a WTP Event Request to send
information to the AC (Section 8.5). The WTP receives a WTP
Event Response from the AC (Section 8.6).
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Data Transfer: The WTP generates a Data Transfer Request to
the AC (Section 8.7). The WTP receives a Data Transfer
Response from the AC (Section 8.8).
WLAN Config Request: The WTP receives a WLAN Config Request
message (Section 11.8.1), to which it MUST respond with a WLAN
Config Response (see Section 11.8.2).
Mobile Config Request: The WTP receives an Mobile Config
Request message (Section 9.1), to which it MUST respond with a
Mobile Config Response (see Section 9.2).
AC: This is the AC's normal state of operation, and there are
many events that cause this to occur:
Configuration Update: The AC sends a Configuration Update
Request (see Section 7.4) to the WTP to update its
configuration. The AC receives a Configuration Update Response
(see Section 7.5) from the WTP.
Change State Event: The AC receives a Change State Event
Request (see Section 7.6), to which it MUST respond with the
Change State Event Response (see Section 7.7).
Echo: The AC sends an Echo Request message (Section 6.5) or
receives the associated Echo Response (see Section 6.6) from
the WTP.
Clear Config Indication: The AC sends a Clear Config
Indication message (Section 7.8).
WLAN Config: The AC sends a WLAN Config Request message
(Section 11.8.1) or receives the associated WLAN Config
Response (see Section 11.8.2) from the WTP.
Mobile Config: The AC sends a Mobile Config Request message
(Section 9.1) or receives the associated Mobile Config Response
(see Section 9.2) from the WTP.
Data Transfer: The AC receives a Data Transfer Request from
the AC (see Section 8.7) and MUST generate the associated Data
Transfer Response message (see Section 8.8).
WTP Event: The AC receives a WTP Event Request from the AC
(see Section 8.5) and MUST generate the associated WTP Event
Response message (see Section 8.6).
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Run to Reset (s): This event occurs when the AC wishes for the WTP
to reboot.
WTP: The WTP enters this state when it receives a Reset Request
(see Section 8.3). It must respond with a Reset Response
(see Section 8.4), and once the reliable transport
acknowledgement has been received, it must reboot itself.
AC: This state transition occurs either through some
administrative action, or via some internal event on the AC
that causes it to request that the WTP disconnect. Note
that the AC itself does not reset, but it places the
specific WTPs context it is communicating with in the reset
state.
Run to Idle (t): This event occurs when an error occurs in the
communication between the WTP and the AC.
WTP: The WTP enters this state when the underlying reliable
transport is unable to transmit a message within the
RetransmitInterval timer (see Section 12), and the maximum
number of RetransmitCount counter has reached the
MaxRetransmit variable (see Section 13).
AC: The AC enters this state when the underlying reliable
transport in unable to transmit a message within the
RetransmitInterval timer (see Section 12), and the maximum
number of RetransmitCount counter has reached the
MaxRetransmit variable (see Section 13).
Run to Key Update (u): This event occurs when the WTP and the AC are
to exchange new keying material, with which it must use to protect
all future messages.
WTP: This state transition occurs when the KeyLifetime timer
expires (see Section 12).
AC: The WTP enters this state when it receives a Key Update
Request (see Section 6.7).
Key Update to Key Confirm (w): This event occurs during the rekey
phase and is used to complete the loop.
WTP: This state transition occurs when the WTP receives the Key
Update Response. The WTP MUST only accept the message if it
is authentic. The WTP responds to this response with a Key
Update ACK.
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AC: The AC enters this state when it receives an authenticated
Key Update ACK message.
Key Confirm to Run (5): This event occurs when the rekey exchange
phase is completed.
WTP: This state transition occurs when the WTP receives the Key
Update Confirm. The newly derived encryption key and
Initialization Vector (IV) must be plumbed into the crypto
module after validating the message's authentication.
AC: The AC enters this state when it transmits the Key Update
Confirm message. The newly derived encryption key and IV
must be plumbed into the crypto module after transmitting a
Key Update Confirm message.
Key Update to Reset (x): This event occurs when the key exchange
phase times out.
WTP: This state transition occurs when the WTP does not receive a
Key Update Response from the AC.
AC: The AC enters this state when it is unable to process a Key
Update Request.
Reset to Idle (y): This event occurs when the state machine is
restarted.
WTP: The WTP reboots itself. After rebooting, the WTP will start
its LWAPP state machine in the Idle state.
AC: The AC clears out any state associated with the WTP. The AC
generally does this as a result of the reliable link layer
timing out.
3. LWAPP Transport Layers
The LWAPP protocol can operate at Layer 2 or 3. For Layer 2 support,
the LWAPP messages are carried in a native Ethernet frame. As such,
the protocol is not routable and depends upon Layer 2 connectivity
between the WTP and the AC. Layer 3 support is provided by
encapsulating the LWAPP messages within UDP.
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3.1. LWAPP Transport Header
All LWAPP protocol packets are encapsulated using a common header
format, regardless of the transport used to carry the frames.
However, certain flags are not applicable for a given transport, and
it is therefore necessary to refer to the specific transport section
in order to determine which flags are valid.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|VER| RID |C|F|L| Frag ID | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status/WLANs | Payload... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.1.1. VER Field
A 2-bit field that contains the version of LWAPP used in this packet.
The value for this document is 0.
3.1.2. RID Field
A 3-bit field that contains the Radio ID number for this packet.
WTPs with multiple radios but a single MAC address use this field to
indicate which radio is associated with the packet.
3.1.3. C Bit
The control message 'C' bit indicates whether this packet carries a
data or control message. When this bit is zero (0), the packet
carries an LWAPP data message in the payload (see Section 4.1). When
this bit is one (1), the packet carries an LWAPP control message as
defined in Section 4.2 for consumption by the addressed destination.
3.1.4. F Bit
The Fragment 'F' bit indicates whether this packet is a fragment.
When this bit is one (1), the packet is a fragment and MUST be
combined with the other corresponding fragments to reassemble the
complete information exchanged between the WTP and AC.
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3.1.5. L Bit
The Not Last 'L' bit is valid only if the 'F' bit is set and
indicates whether the packet contains the last fragment of a
fragmented exchange between the WTP and AC. When this bit is 1, the
packet is not the last fragment. When this bit is 0, the packet is
the last fragment.
3.1.6. Fragment ID
An 8-bit field whose value is assigned to each group of fragments
making up a complete set. The Fragment ID space is managed
individually for every WTP/AC pair. The value of Fragment ID is
incremented with each new set of fragments. The Fragment ID wraps to
zero after the maximum value has been used to identify a set of
fragments. LWAPP only supports up to 2 fragments per frame.
3.1.7. Length
The 16-bit length field contains the number of bytes in the Payload.
The field is encoded as an unsigned number. If the LWAPP packet is
encrypted, the length field includes the Advanced Encryption Standard
Counter with CBC-MAC (AES-CCM) MIC (see Section 10.2 for more
information).
3.1.8. Status and WLANS
The interpretation of this 16-bit field is binding-specific. Refer
to the transport portion of the binding for a wireless technology for
the specification.
3.1.9. Payload
This field contains the header for an LWAPP data message or LWAPP
control message, followed by the data associated with that message.
3.2. Using IEEE 802.3 MAC as LWAPP Transport
This section describes how the LWAPP protocol is provided over native
Ethernet frames. An LWAPP packet is formed from the MAC frame
header, followed by the LWAPP message header. The following figure
provides an example of the frame formats used when LWAPP is used over
the IEEE 802.3 transport.
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Layer 2 LWAPP Data Frame
+-----------------------------------------------------------+
| MAC Header | LWAPP Header [C=0] | Forwarded Data ... |
+-----------------------------------------------------------+
Layer 2 LWAPP Control Frame
+---------------------------------------------------+
| MAC Header | LWAPP Header [C=1] | Control Message |
+---------------------------------------------------+
| Message Elements ... |
+----------------------+
3.2.1. Framing
Source Address
A MAC address belonging to the interface from which this message is
sent. If multiple source addresses are configured on an interface,
then the one chosen is implementation-dependent.
Destination Address
A MAC address belonging to the interface to which this message is to
be sent. This destination address MAY be either an individual
address or a multicast address, if more than one destination
interface is intended.
Ethertype
The Ethertype field is set to 0x88bb.
3.2.2. AC Discovery
When run over IEEE 802.3, LWAPP messages are distributed to a
specific MAC-level broadcast domain. The AC discovery mechanism used
with this transport is for a WTP to transmit a Discovery Request
message to a broadcast destination MAC address. The ACs will receive
this message and reply based on their policy.
3.2.3. LWAPP Message Header Format over IEEE 802.3 MAC Transport
All of the fields described in Section 3.1 are used when LWAPP uses
the IEEE 802.3 MAC transport.
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3.2.4. Fragmentation/Reassembly
Fragmentation at the MAC layer is managed using the F, L, and Frag ID
fields of the LWAPP message header. The LWAPP protocol only allows a
single packet to be fragmented into 2, which is sufficient for a
frame that exceeds MTU due to LWAPP encapsulation. When used with
Layer 2 (Ethernet) transport, both fragments MUST include the LWAPP
header.
3.2.5. Multiplexing
LWAPP control messages and data messages are distinguished by the 'C'
bit in the LWAPP message header.
3.3. Using IP/UDP as LWAPP Transport
This section defines how LWAPP makes use of IP/UDP transport between
the WTP and the AC. When this transport is used, the MAC layer is
controlled by the IP stack, and there are therefore no special MAC-
layer requirements. The following figure provides an example of the
frame formats used when LWAPP is used over the IP/UDP transport. IP
stacks can be either IPv4 or IPv6.
Layer 3 LWAPP Data Frame
+--------------------------------------------+
| MAC Header | IP | UDP | LWAPP Header [C=0] |
+--------------------------------------------+
|Forwarded Data ... |
+-------------------+
Layer 3 LWAPP Control Frame
+--------------------------------------------+
| MAC Header | IP | UDP | LWAPP Header [C=1] |
+--------------------------------------------+
| Control Message | Message Elements ... |
+-----------------+----------------------+
3.3.1. Framing
Communication between the WTP and AC is established according to the
standard UDP client/server model. The connection is initiated by the
WTP (client) to the well-known UDP port of the AC (server) used for
control messages. This UDP port number of the AC is 12222 for LWAPP
data and 12223 for LWAPP control frames.
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3.3.2. AC Discovery
When LWAPP is run over routed IP networks, the WTP and the AC do not
need to reside in the same IP subnet (broadcast domain). However, in
the event the peers reside on separate subnets, there must exist a
mechanism for the WTP to discover the AC.
As the WTP attempts to establish communication with the AC, it sends
the Discovery Request message and receives the corresponding response
message from the AC. The WTP must send the Discovery Request message
to either the limited broadcast IP address (255.255.255.255), a well
known multicast address, or the unicast IP address of the AC. Upon
receipt of the message, the AC issues a Discovery Response message to
the unicast IP address of the WTP, regardless of whether a Discovery
Request was sent as a broadcast, multicast, or unicast message.
Whether the WTP uses a limited IP broadcast, multicast or unicast IP
address is implementation-dependent.
In order for a WTP to transmit a Discovery Request to a unicast
address, the WTP must first obtain the IP address of the AC. Any
static configuration of an AC's IP address on the WTP non-volatile
storage is implementation-dependent. However, additional dynamic
schemes are possible: for example:
DHCP: A comma-delimited, ASCII-encoded list of AC IP addresses is
embedded inside a DHCP vendor-specific option 43 extension.
An example of the actual format of the vendor-specific payload
for IPv4 is of the form "10.1.1.1, 10.1.1.2".
DNS: The DNS name "LWAPP-AC-Address" MAY be resolvable to one or
more AC addresses.
3.3.3. LWAPP Message Header Format over IP/UDP Transport
All of the fields described in Section 3.1 are used when LWAPP uses
the IPv4/UDP or IPv6/UDP transport, with the following exceptions.
3.3.3.1. F Bit
This flag field is not used with this transport, and MUST be set to
zero.
3.3.3.2. L Bit
This flag field is not used with this transport, and MUST be set to
zero.
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3.3.3.3. Frag ID
This field is not used with this transport, and MUST be set to zero.
3.3.4. Fragmentation/Reassembly for IPv4
When LWAPP is implemented at L3, the transport layer uses IP
fragmentation to fragment and reassemble LWAPP messages that are
longer than the MTU size used by either the WTP or AC. The details
of IP fragmentation are covered in [8]. When used with the IP
transport, only the first fragment would include the LWAPP header.
3.3.5. Fragmentation/Reassembly for IPv6
IPv6 does MTU discovery so fragmentation and re-assembly is not
necessary for UDP packets.
3.3.6. Multiplexing
LWAPP messages convey control information between WTP and AC, as well
as binding specific data frames or binding specific management
frames. As such, LWAPP messages need to be multiplexed in the
transport sub-layer and be delivered to the proper software entities
in the endpoints of the protocol. However, the 'C' bit is still used
to differentiate between data and control frames.
In case of Layer 3 connection, multiplexing is achieved by use of
different UDP ports for control and data packets (see Section 3.3.1).
As part of the Join procedure, the WTP and AC may negotiate different
IP Addresses for data or control messages. The IP address returned
in the AP Manager Control IP Address message element is used to
inform the WTP with the IP address to which it must send all control
frames. The AP Manager Data IP Address message element MAY be
present only if the AC has a different IP address that the WTP is to
use to send its data LWAPP frames.
In the event the WTP and AC are separated by a NAT, with the WTP
using private IP address space, it is the responsibility of the NAT
to manage appropriate UDP port mapping.
4. LWAPP Packet Definitions
This section contains the packet types and format. The LWAPP
protocol is designed to be transport-agnostic by specifying packet
formats for both MAC frames and IP packets. An LWAPP packet consists
of an LWAPP Transport Layer packet header followed by an LWAPP
message.
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Transport details can be found in Section 3.
4.1. LWAPP Data Messages
An LWAPP data message is a forwarded wireless frame. When forwarding
wireless frames, the sender simply encapsulates the wireless frame in
an LWAPP data packet, using the appropriate transport rules defined
in Section 3.
In the event that the encapsulated frame would exceed the transport
layer's MTU, the sender is responsible for the fragmentation of the
frame, as specified in the transport-specific section of Section 3.
The actual format of the encapsulated LWAPP data frame is subject to
the rules defined under the specific wireless technology binding.
4.2. LWAPP Control Messages Overview
The LWAPP Control protocol provides a control channel between the WTP
and the AC. The control channel is the series of control messages
between the WTP and AC, associated with a session ID and key.
Control messages are divided into the following distinct message
types:
Discovery: LWAPP Discovery messages are used to identify potential
ACs, their load and capabilities.
Control Channel Management: Messages that fall within this
classification are used for the discovery of ACs by the WTPs as
well as the establishment and maintenance of an LWAPP control
channel.
WTP Configuration: The WTP Configuration messages are used by the AC
to push a specific configuration to the WTPs with which it has a
control channel. Messages that deal with the retrieval of
statistics from the WTP also fall in this category.
Mobile Session Management: Mobile Session Management messages are
used by the AC to push specific mobile policies to the WTP.
Firmware Management: Messages in this category are used by the AC to
push a new firmware image down to the WTP.
Control Channel, WTP Configuration, and Mobile Session Management
MUST be implemented. Firmware Management MAY be implemented.
In addition, technology-specific bindings may introduce new control
channel commands that depart from the above list.
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4.2.1. Control Message Format
All LWAPP control messages are sent encapsulated within the LWAPP
header (see Section 3.1). Immediately following the header is the
LWAPP control header, which has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type | Seq Num | Msg Element Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Msg Element [0..N] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.2.1.1. Message Type
The Message Type field identifies the function of the LWAPP control
message. The valid values for a Message Type are the following:
Description Value
Discovery Request 1
Discovery Response 2
Join Request 3
Join Response 4
Join ACK 5
Join Confirm 6
Unused 7-9
Configure Request 10
Configure Response 11
Configuration Update Request 12
Configuration Update Response 13
WTP Event Request 14
WTP Event Response 15
Change State Event Request 16
Change State Event Response 17
Unused 18-21
Echo Request 22
Echo Response 23
Image Data Request 24
Image Data Response 25
Reset Request 26
Reset Response 27
Unused 28-29
Key Update Request 30
Key Update Response 31
Primary Discovery Request 32
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Primary Discovery Response 33
Data Transfer Request 34
Data Transfer Response 35
Clear Config Indication 36
WLAN Config Request 37
WLAN Config Response 38
Mobile Config Request 39
Mobile Config Response 40
4.2.1.2. Sequence Number
The Sequence Number field is an identifier value to match request/
response packet exchanges. When an LWAPP packet with a request
message type is received, the value of the Sequence Number field is
copied into the corresponding response packet.
When an LWAPP control frame is sent, its internal sequence number
counter is monotonically incremented, ensuring that no two requests
pending have the same sequence number. This field will wrap back to
zero.
4.2.1.3. Message Element Length
The length field indicates the number of bytes following the Session
ID field. If the LWAPP packet is encrypted, the length field
includes the AES-CCM MIC (see Section 10.2 for more information).
4.2.1.4. Session ID
The Session ID is a 32-bit unsigned integer that is used to identify
the security context for encrypted exchanges between the WTP and the
AC. Note that a Session ID is a random value that MUST be unique
between a given AC and any of the WTPs with which it may be
communicating.
4.2.1.5. Message Element [0..N]
The message element(s) carry the information pertinent to each of the
control message types. Every control message in this specification
specifies which message elements are permitted.
4.2.2. Message Element Format
The message element is used to carry information pertinent to a
control message. Every message element is identified by the Type
field, whose numbering space is managed via IANA (see Section 16).
The total length of the message elements is indicated in the Message
Element Length field.
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All of the message element definitions in this document use a diagram
similar to the one below in order to depict their formats. Note that
in order to simplify this specification, these diagrams do not
include the header fields (Type and Length). However, in each
message element description, the header's field values will be
defined.
Note that additional message elements may be defined in separate IETF
documents.
The format of a message element uses the TLV format shown here:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where Type (8 bits) identifies the character of the information
carried in the Value field and Length (16 bits) indicates the number
of bytes in the Value field.
4.2.2.1. Generic Message Elements
This section includes message elements that are not bound to a
specific control message.
4.2.2.1.1. Vendor Specific
The Vendor-Specific Payload is used to communicate vendor-specific
information between the WTP and the AC. The value contains the
following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Element ID | Value... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 104 for Vendor Specific
Length: >= 7
Vendor Identifier: A 32-bit value containing the IANA-assigned "SMI
Network Management Private Enterprise Codes" [13].
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Element ID: A 16-bit Element Identifier that is managed by the
vendor.
Value: The value associated with the vendor-specific element.
4.2.3. Quality of Service
It is recommended that LWAPP control messages be sent by both the AC
and the WTP with an appropriate Quality-of-Service precedence value,
ensuring that congestion in the network minimizes occurrences of
LWAPP control channel disconnects. Therefore, a Quality-of-Service-
enabled LWAPP device should use:
802.1P: The precedence value of 7 SHOULD be used.
DSCP: The Differentiated Services Code Point (DSCP) tag value of 46
SHOULD be used.
5. LWAPP Discovery Operations
The Discovery messages are used by a WTP to determine which ACs are
available to provide service, as well as the capabilities and load of
the ACs.
5.1. Discovery Request
The Discovery Request is used by the WTP to automatically discover
potential ACs available in the network. A WTP must transmit this
command even if it has a statically configured AC, as it is a
required step in the LWAPP state machine.
Discovery Requests MUST be sent by a WTP in the Discover state after
waiting for a random delay less of than MaxDiscoveryInterval, after a
WTP first comes up or is (re)initialized. A WTP MUST send no more
than a maximum of MaxDiscoveries discoveries, waiting for a random
delay less than MaxDiscoveryInterval between each successive
discovery.
This is to prevent an explosion of WTP Discoveries. An example of
this occurring would be when many WTPs are powered on at the same
time.
Discovery Requests MUST be sent by a WTP when no Echo Responses are
received for NeighborDeadInterval and the WTP returns to the Idle
state. Discovery Requests are sent after NeighborDeadInterval, they
MUST be sent after waiting for a random delay less than
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MaxDiscoveryInterval. A WTP MAY send up to a maximum of
MaxDiscoveries discoveries, waiting for a random delay less than
MaxDiscoveryInterval between each successive discovery.
If a Discovery Response is not received after sending the maximum
number of Discovery Requests, the WTP enters the Sulking state and
MUST wait for an interval equal to SilentInterval before sending
further Discovery Requests.
The Discovery Request message may be sent as a unicast, broadcast, or
multicast message.
Upon receiving a Discovery Request, the AC will respond with a
Discovery Response sent to the address in the source address of the
received Discovery Request.
The following subsections define the message elements that MUST be
included in this LWAPP operation.
5.1.1. Discovery Type
The Discovery message element is used to configure a WTP to operate
in a specific mode.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Discovery Type|
+-+-+-+-+-+-+-+-+
Type: 58 for Discovery Type
Length: 1
Discovery Type: An 8-bit value indicating how the AC was
discovered. The following values are supported:
0 - Broadcast
1 - Configured
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5.1.2. WTP Descriptor
The WTP Descriptor message element is used by the WTP to communicate
its current hardware/firmware configuration. The value contains the
following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hardware Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Software Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Boot Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max Radios | Radios in use | Encryption Capabilities |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 3 for WTP Descriptor
Length: 16
Hardware Version: A 32-bit integer representing the WTP's hardware
version number.
Software Version: A 32-bit integer representing the WTP's Firmware
version number.
Boot Version: A 32-bit integer representing the WTP's boot loader's
version number.
Max Radios: An 8-bit value representing the number of radios (where
each radio is identified via the RID field) supported by the WTP.
Radios in Use: An 8-bit value representing the number of radios
present in the WTP.
Encryption Capabilities: This 16-bit field is used by the WTP to
communicate its capabilities to the AC. Since most WTPs support
link-layer encryption, the AC may make use of these services.
There are binding-dependent encryption capabilites. A WTP that
does not have any encryption capabilities would set this field to
zero (0). Refer to the specific binding for the specification.
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5.1.3. WTP Radio Information
The WTP Radio Information message element is used to communicate the
radio information in a specific slot. The Discovery Request MUST
include one such message element per radio in the WTP. The Radio-
Type field is used by the AC in order to determine which technology-
specific binding is to be used with the WTP.
The value contains two fields, as shown:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Radio Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 4 for WTP Radio Information
Length: 2
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP.
Radio Type: The type of radio present. The following values are
supported:
1 - 802.11bg: An 802.11bg radio.
2 - 802.11a: An 802.11a radio.
3 - 802.16: An 802.16 radio.
4 - Ultra Wideband: A UWB radio.
7 - all: Used to specify all radios in the WTP.
5.2. Discovery Response
The Discovery Response is a mechanism by which an AC advertises its
services to requesting WTPs.
Discovery Responses are sent by an AC after receiving a Discovery
Request.
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When a WTP receives a Discovery Response, it MUST wait for an
interval not less than DiscoveryInterval for receipt of additional
Discovery Responses. After the DiscoveryInterval elapses, the WTP
enters the Joining state and will select one of the ACs that sent a
Discovery Response and send a Join Request to that AC.
The following subsections define the message elements that MUST be
included in this LWAPP operation.
5.2.1. AC Address
The AC Address message element is used to communicate the identity of
the AC. The value contains two fields, as shown:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 2 for AC Address
Length: 7
Reserved: MUST be set to zero
MAC Address: The MAC address of the AC
5.2.2. AC Descriptor
The AC Descriptor message element is used by the AC to communicate
its current state. The value contains the following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Hardware Version ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HW Ver | Software Version ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SW Ver | Stations | Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Limit | Radios | Max Radio |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max Radio | Security |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 6 for AC Descriptor
Length: 17
Reserved: MUST be set to zero
Hardware Version: A 32-bit integer representing the AC's hardware
version number.
Software Version: A 32-bit integer representing the AC's Firmware
version number.
Stations: A 16-bit integer representing the number of mobile
stations currently associated with the AC.
Limit: A 16-bit integer representing the maximum number of stations
supported by the AC.
Radios: A 16-bit integer representing the number of WTPs currently
attached to the AC.
Max Radio: A 16-bit integer representing the maximum number of WTPs
supported by the AC.
Security: An 8-bit bitmask specifying the security schemes
supported by the AC. The following values are supported (see
Section 10):
1 - X.509 Certificate-Based
2 - Pre-Shared Secret
5.2.3. AC Name
The AC Name message element contains an ASCII representation of the
AC's identity. The value is a variable-length byte string. The
string is NOT zero terminated.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Name ...
+-+-+-+-+-+-+-+-+
Type: 31 for AC Name
Length: > 0
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Name: A variable-length ASCII string containing the AC's name.
5.2.4. WTP Manager Control IPv4 Address
The WTP Manager Control IPv4 Address message element is sent by the
AC to the WTP during the discovery process and is used by the AC to
provide the interfaces available on the AC, and their current load.
This message element is useful for the WTP to perform load balancing
across multiple interfaces.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 99 for WTP Manager Control IPv4 Address
Length: 6
IP Address: The IP address of an interface.
WTP Count: The number of WTPs currently connected to the interface.
5.2.5. WTP Manager Control IPv6 Address
The WTP Manager Control IPv6 Address message element is sent by the
AC to the WTP during the discovery process and is used by the AC to
provide the interfaces available on the AC, and their current load.
This message element is useful for the WTP to perform load balancing
across multiple interfaces.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 137 for WTP Manager Control IPv6 Address
Length: 6
IP Address: The IP address of an interface.
WTP Count: The number of WTPs currently connected to the interface.
5.3. Primary Discovery Request
The Primary Discovery Request is sent by the WTP in order to
determine whether its preferred (or primary) AC is available.
Primary Discovery Requests are sent by a WTP when it has a primary AC
configured, and is connected to another AC. This generally occurs as
a result of a failover, and is used by the WTP as a means to discover
when its primary AC becomes available. As a consequence, this
message is only sent by a WTP when it is in the Run state.
The frequency of the Primary Discovery Requests should be no more
often than the sending of the Echo Request message.
Upon receiving a Discovery Request, the AC will respond with a
Primary Discovery Response sent to the address in the source address
of the received Primary Discovery Request.
The following subsections define the message elements that MUST be
included in this LWAPP operation.
5.3.1. Discovery Type
The Discovery Type message element is defined in Section 5.1.1.
5.3.2. WTP Descriptor
The WTP Descriptor message element is defined in Section 5.1.2.
5.3.3. WTP Radio Information
A WTP Radio Information message element must be present for every
radio in the WTP. This message element is defined in Section 5.1.3.
5.4. Primary Discovery Response
The Primary Discovery Response is a mechanism by which an AC
advertises its availability and services to requesting WTPs that are
configured to have the AC as its primary AC.
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Primary Discovery Responses are sent by an AC after receiving a
Primary Discovery Request.
When a WTP receives a Primary Discovery Response, it may opt to
establish an LWAPP connection to its primary AC, based on the
configuration of the WTP Fallback Status message element on the WTP.
The following subsections define the message elements that MUST be
included in this LWAPP operation.
5.4.1. AC Descriptor
The Discovery Type message element is defined in Section 5.2.2.
5.4.2. AC Name
The AC Name message element is defined in Section 5.2.3.
5.4.3. WTP Manager Control IPv4 Address
A WTP Radio Information message element MAY be present for every
radio in the WTP that is reachable via IPv4. This message element is
defined in Section 5.2.4.
5.4.4. WTP Manager Control IPv6 Address
A WTP Radio Information message element must be present for every
radio in the WTP that is reachable via IPv6. This message element is
defined in Section 5.2.5.
6. Control Channel Management
The Control Channel Management messages are used by the WTP and AC to
create and maintain a channel of communication on which various other
commands may be transmitted, such as configuration, firmware update,
etc.
6.1. Join Request
The Join Request is used by a WTP to inform an AC that it wishes to
provide services through it.
Join Requests are sent by a WTP in the Joining state after receiving
one or more Discovery Responses. The Join Request is also used as an
MTU discovery mechanism by the WTP. The WTP issues a Join Request
with a Test message element, bringing the total size of the message
to exceed MTU.
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If the transport used does not provide MTU path discovery, the
initial Join Request is padded with the Test message element to 1596
bytes. If a Join Response is received, the WTP can forward frames
without requiring any fragmentation. If no Join Response is
received, it issues a second Join Request padded with the Test
payload to a total of 1500 bytes. The WTP continues to cycle from
large (1596) to small (1500) packets until a Join Response has been
received, or until both packets' sizes have been retransmitted 3
times. If the Join Response is not received after the maximum number
of retransmissions, the WTP MUST abandon the AC and restart the
discovery phase.
When an AC receives a Join Request, it will respond with a Join
Response. If the certificate-based security mechanism is used, the
AC validates the certificate found in the request. If valid, the AC
generates a session key that will be used to secure the control
frames it exchanges with the WTP. When the AC issues the Join
Response, the AC creates a context for the session with the WTP.
If the pre-shared session key security mechanism is used, the AC
saves the WTP's nonce, found in the WNonce message element, and
creates its own nonce, which it includes in the ANonce message
element. Finally, the AC creates the PSK-MIC, which is computed
using a key that is derived from the PSK.
A Join Request that includes both a WNonce and a Certificate message
element MUST be considered invalid.
Details on the key generation are found in Section 10.
The following subsections define the message elements that MUST be
included in this LWAPP operation.
6.1.1. WTP Descriptor
The WTP Descriptor message element is defined in Section 5.1.2.
6.1.2. AC Address
The AC Address message element is defined in Section 5.2.1.
6.1.3. WTP Name
The WTP Name message element value is a variable-length byte string.
The string is NOT zero terminated.
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0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Name ...
+-+-+-+-+-+-+-+-+
Type: 5 for WTP Name
Length: > 0
Name: A non-zero-terminated string containing the WTP's name.
6.1.4. Location Data
The Location Data message element is a variable-length byte string
containing user-defined location information (e.g., "Next to
Fridge"). The string is NOT zero terminated.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Location ...
+-+-+-+-+-+-+-+-+
Type: 35 for Location Data
Length: > 0
Location: A non-zero-terminated string containing the WTP's
location.
6.1.5. WTP Radio Information
A WTP Radio Information message element must be present for every
radio in the WTP. This message element is defined in Section 5.1.3.
6.1.6. Certificate
The Certificate message element value is a byte string containing a
DER-encoded x.509v3 certificate. This message element is only
included if the LWAPP security type used between the WTP and the AC
makes use of certificates (see Section 10 for more information).
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Certificate...
+-+-+-+-+-+-+-+-+
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Type: 44 for Certificate
Length: > 0
Certificate: A non-zero-terminated string containing the device's
certificate.
6.1.7. Session ID
The Session ID message element value contains a randomly generated
[4] unsigned 32-bit integer.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 45 for Session ID
Length: 4
Session ID: 32-bit random session identifier.
6.1.8. Test
The Test message element is used as padding to perform MTU discovery,
and it MAY contain any value, of any length.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Padding ...
+-+-+-+-+-+-+-+-+
Type: 18 for Test
Length: > 0
Padding: A variable-length pad.
6.1.9. XNonce
The XNonce is used by the WTP to communicate its random nonce during
the join or rekey phase. See Section 10 for more information.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 111 for XNonce
Length: 16
Nonce: 1 16-octet random nonce.
6.2. Join Response
The Join Response is sent by the AC to indicate to a WTP whether it
is capable and willing to provide service to it.
Join Responses are sent by the AC after receiving a Join Request.
Once the Join Response has been sent, the Heartbeat timer is
initiated for the session to EchoInterval. Expiration of the timer
will result in deletion of the AC-WTP session. The timer is
refreshed upon receipt of the Echo Request.
If the security method used is certificate-based, when a WTP receives
a Join Response, it enters the Joined state and initiates either a
Configure Request or Image Data to the AC to which it is now joined.
Upon entering the Joined state, the WTP begins timing an interval
equal to NeighborDeadInterval. Expiration of the timer will result
in the transmission of the Echo Request.
If the security method used is pre-shared-secret-based, when a WTP
receives a Join Response that includes a valid PSK-MIC message
element, it responds with a Join ACK that also MUST include a locally
computed PSK-MIC message element.
The following subsections define the message elements that MUST be
included in this LWAPP operation.
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6.2.1. Result Code
The Result Code message element value is a 32-bit integer value,
indicating the result of the request operation corresponding to the
sequence number in the message. The Result Code is included in a
successful Join Response.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Result Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 2 for Result Code
Length: 4
Result Code: The following values are defined:
0 Success
1 Failure (AC List message element MUST be present)
6.2.2. Status
The Status message element is sent by the AC to the WTP in a non-
successful Join Response message. This message element is used to
indicate the reason for the failure and should only be accompanied
with a Result Code message element that indicates a failure.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Status |
+-+-+-+-+-+-+-+-+
Type: 60 for Status
Length: 1
Status: The Status field indicates the reason for an LWAPP failure.
The following values are supported:
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1 - Reserved - do not use
2 - Resource Depletion
3 - Unknown Source
4 - Incorrect Data
6.2.3. Certificate
The Certificate message element is defined in Section 6.1.6. Note
this message element is only included if the WTP and the AC make use
of certificate-based security as defined in Section 10.
6.2.4. WTP Manager Data IPv4 Address
The WTP Manager Data IPv4 Address message element is optionally sent
by the AC to the WTP during the join phase. If present, the IP
Address contained in this message element is the address the WTP is
to use when sending any of its LWAPP data frames.
Note that this message element is only valid when LWAPP uses the
IP/UDP Layer 3 transport.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 138 for WTP Manager Data IPv4 Address
Length: 4
IP Address: The IP address of an interface.
6.2.5. WTP Manager Data IPv6 Address
The WTP Manager Data IPv6 Address message element is optionally sent
by the AC to the WTP during the join phase. If present, the IP
Address contained in this message element is the address the WTP is
to use when sending any of its LWAPP data frames.
Note that this message element is only valid when LWAPP uses the
IP/UDP Layer 3 transport.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 139 for WTP Manager Data IPv6 Address
Length: 4
IP Address: The IP address of an interface.
6.2.6. AC IPv4 List
The AC List message element is used to configure a WTP with the
latest list of ACs in a cluster. This message element MUST be
included if the Join Response returns a failure indicating that the
AC cannot handle the WTP at this time, allowing the WTP to find an
alternate AC to which to connect.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC IP Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 59 for AC List
Length: >= 4
AC IP Address: An array of 32-bit integers containing an AC's IPv4
Address.
6.2.7. AC IPv6 List
The AC List message element is used to configure a WTP with the
latest list of ACs in a cluster. This message element MUST be
included if the Join Response returns a failure indicating that the
AC cannot handle the WTP at this time, allowing the WTP to find an
alternate AC to which to connect.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC IP Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC IP Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC IP Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC IP Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 141 for AC List
Length: >= 4
AC IP Address: An array of 32-bit integers containing an AC's IPv6
Address.
6.2.8. ANonce
The ANonce message element is sent by an AC during the join or rekey
phase. The contents of the ANonce are encrypted as described in
Section 10 for more information.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 108 for ANonce
Length: 16
Nonce: An encrypted, 16-octet random nonce.
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6.2.9. PSK-MIC
The PSK-MIC message element includes a message integrity check, whose
purpose is to provide confirmation to the peer that the sender has
the proper session key. This message element is only included if the
security method used between the WTP and the AC is the pre-shared
secret mechanism. See Section 10 for more information.
When present, the PSK-MIC message element MUST be the last message
element in the message. The MIC is computed over the complete LWAPP
packet, from the LWAPP control header as defined in Section 4.2.1 to
the end of the packet (which MUST be this PSK-MIC message element).
The MIC field in this message element and the Sequence Number field
in the LWAPP control header MUST be set to zeroes prior to computing
the MIC. The length field in the LWAPP control header must already
include this message element prior to computing the MIC.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPI | MIC ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 109 for PSK-MIC
Length: > 1
SPI: The Security Parameter Index (SPI) field specifies the
cryptographic algorithm used to create the message integrity
check. The following values are supported:
0 - Unused
1 - HMAC-SHA-1 (RFC 2104 [15])
MIC: A 20-octet Message Integrity Check.
6.3. Join ACK
The Join ACK message is sent by the WTP upon receiving a Join
Response, which has a valid PSK-MIC message element, as a means of
providing key confirmation to the AC. The Join ACK is only used in
the case where the WTP makes use of the pre-shared key LWAPP mode
(see Section 10 for more information).
Note that the AC should never receive this message unless the
security method used between the WTP and the AC is pre-shared-secret-
based.
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The following subsections define the message elements that MUST be
included in this LWAPP operation.
6.3.1. Session ID
The Session ID message element is defined in Section 6.1.7.
6.3.2. WNonce
The WNonce message element is sent by a WTP during the join or rekey
phase. The contents of the ANonce are encrypted as described in
Section 10 for more information.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 107 for WNonce
Length: 16
Nonce: An encrypted, 16-octet random nonce.
6.3.3. PSK-MIC
The PSK-MIC message element is defined in Section 6.2.9.
6.4. Join Confirm
The Join Confirm message is sent by the AC upon receiving a Join ACK,
which has a valid PSK-MIC message element, as a means of providing
key confirmation to the WTP. The Join Confirm is only used in the
case where the WTP makes use of the pre-shared key LWAPP mode (see
Section 10 for more information).
If the security method used is pre-shared-key-based, when a WTP
receives a Join Confirm, it enters the Joined state and initiates
either a Configure Request or Image Data to the AC to which it is now
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joined. Upon entering the Joined state, the WTP begins timing an
interval equal to NeighborDeadInterval. Expiration of the timer will
result in the transmission of the Echo Request.
This message is never received, or sent, when the security type used
between the WTP and the AC is certificated-based.
The following subsections define the message elements that MUST be
included in this LWAPP operation.
6.4.1. Session ID
The Session ID message element is defined in Section 6.1.7.
6.4.2. PSK-MIC
The PSK-MIC message element is defined in Section 6.2.9.
6.5. Echo Request
The Echo Request message is a keepalive mechanism for the LWAPP
control message.
Echo Requests are sent periodically by a WTP in the Run state (see
Figure 2) to determine the state of the connection between the WTP
and the AC. The Echo Request is sent by the WTP when the Heartbeat
timer expires, and it MUST start its NeighborDeadInterval timer.
The Echo Request carries no message elements.
When an AC receives an Echo Request, it responds with an Echo
Response.
6.6. Echo Response
The Echo Response acknowledges the Echo Request, and is only accepted
while in the Run state (see Figure 2).
Echo Responses are sent by an AC after receiving an Echo Request.
After transmitting the Echo Response, the AC should reset its
Heartbeat timer to expire in the value configured for EchoInterval.
If another Echo request is not received by the AC when the timer
expires, the AC SHOULD consider the WTP to no longer be reachable.
The Echo Response carries no message elements.
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When a WTP receives an Echo Response it stops the
NeighborDeadInterval timer, and starts the Heartbeat timer to
EchoInterval.
If the NeighborDeadInterval timer expires prior to receiving an Echo
Response, the WTP enters the Idle state.
6.7. Key Update Request
The Key Update Request is used by the WTP to initiate the rekeying
phase. This message is sent by a WTP when in the Run state and MUST
include a new unique Session Identifier. This message MUST also
include a unique nonce in the XNonce message element, which is used
to protect against replay attacks (see Section 10).
The following subsections define the message elements that MUST be
included in this LWAPP operation.
6.7.1. Session ID
The Session ID message element is defined in Section 6.1.7.
6.7.2. XNonce
The XNonce message element is defined in Section 6.1.9.
6.8. Key Update Response
The Key Update Response is sent by the AC in response to the request
message, and includes an encrypted ANonce, which is used to derive
new session keys. This message MUST include a Session Identifier
message element, whose value MUST be identical to the one found in
the Key Update Request.
The AC MUST include a PSK-MIC message element, which provides message
integrity over the whole message.
The following subsections define the message elements that MUST be
included in this LWAPP operation.
6.8.1. Session ID
The Session ID message element is defined in Section 6.1.7.
6.8.2. ANonce
The ANonce message element is defined in Section 6.2.8.
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6.8.3. PSK-MIC
The PSK-MIC message element is defined in Section 6.2.9.
6.9. Key Update ACK
The Key Update ACK is sent by the WTP and includes an encrypted
version of the WTP's nonce, which is used in the key derivation
process. The session keys derived are then used as new LWAPP control
message encryption keys (see Section 10).
The WTP MUST include a PSK-MIC message element, which provides
message integrity over the whole message.
The following subsections define the message elements that MUST be
included in this LWAPP operation.
6.9.1. WNonce
The WNonce message element is defined in Section 6.3.2.
6.9.2. PSK-MIC
The PSK-MIC message element is defined in Section 6.2.9.
6.10. Key Update Confirm
The Key Update Confirm closes the rekeying loop, and allows the WTP
to recognize that the AC has received and processed the Key Update
messages. At this point, the WTP updates its session key in its
crypto engine, and the associated Initialization Vector, ensuring
that all future LWAPP control frames are encrypted with the newly
derived encryption key.
The WTP MUST include a PSK-MIC message element, which provides
message integrity over the whole message.
The following subsections define the message elements that MUST be
included in this LWAPP operation.
6.10.1. PSK-MIC
The PSK-MIC message element is defined in Section 6.2.9.
6.11. Key Update Trigger
The Key Update Trigger is used by the AC to request that a Key Update
Request be initiated by the WTP.
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Key Update Triggers are sent by an AC in the Run state to inform the
WTP to initiate a Key Update Request message.
When a WTP receives a Key Update Trigger, it generates a Key Update
Request.
The following subsections define the message elements that MUST be
included in this LWAPP operation.
6.11.1. Session ID
The Session ID message element is defined in Section 6.1.7.
7. WTP Configuration Management
The Wireless Termination Point Configuration messages are used to
exchange configuration between the AC and the WTP.
7.1. Configuration Consistency
The LWAPP protocol provides flexibility in how WTP configuration is
managed. To put it simply, a WTP has one of two options:
1. The WTP retains no configuration and simply abides by the
configuration provided by the AC.
2. The WTP retains the configuration of parameters provided by the AC
that are non-default values.
If the WTP opts to save configuration locally, the LWAPP protocol
state machine defines the "Configure" state, which is used during the
initial binding WTP-AC phase, which allows for configuration
exchange. During this period, the WTP sends its current
configuration overrides to the AC via the Configure Request message.
A configuration override is a parameter that is non-default. One
example is that in the LWAPP protocol, the default antenna
configuration is an internal-omni antenna. However, a WTP that
either has no internal antennas, or has been explicitely configured
by the AC to use external antennas would send its antenna
configuration during the configure phase, allowing the AC to become
aware of the WTP's current configuration.
Once the WTP has provided its configuration to the AC, the AC sends
down its own configuration. This allows the WTP to inherit the
configuration and policies on the AC.
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An LWAPP AC maintains a copy of each active WTP's configuration.
There is no need for versioning or other means to identify
configuration changes. If a WTP becomes inactive, the AC MAY delete
the configuration associated with it. If a WTP were to fail, and
connect to a new AC, it would provide its overridden configuration
parameters, allowing the new AC to be aware of the WTP's
configuration.
As a consequence, this model allows for resiliency, whereby in light
of an AC failure, another AC could provide service to the WTP. In
this scenario, the new AC would be automatically updated on any
possible WTP configuration changes -- eliminating the need for Inter-
AC communication or the need for all ACs to be aware of the
configuration of all WTPs in the network.
Once the LWAPP protocol enters the Run state, the WTPs begin to
provide service. However, it is quite common for administrators to
require that configuration changes be made while the network is
operational. Therefore, the Configuration Update Request is sent by
the AC to the WTP in order to make these changes at run-time.
7.2. Configure Request
The Configure Request message is sent by a WTP to send its current
configuration to its AC.
Configure Requests are sent by a WTP after receiving a Join Response,
while in the Configure state.
The Configure Request carries binding-specific message elements.
Refer to the appropriate binding for the definition of this
structure.
When an AC receives a Configure Request, it will act upon the content
of the packet and respond to the WTP with a Configure Response.
The Configure Request includes multiple Administrative State message
elements. There is one such message element for the WTP, and then
one per radio in the WTP.
The following subsections define the message elements that MUST be
included in this LWAPP operation.
7.2.1. Administrative State
The Administrative Event message element is used to communicate the
state of a particular radio. The value contains the following
fields.
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Admin State |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 27 for Administrative State
Length: 2
Radio ID: An 8-bit value representing the radio to configure. The
Radio ID field may also include the value of 0xff, which is used
to identify the WTP itself. Therefore, if an AC wishes to change
the administrative state of a WTP, it would include 0xff in the
Radio ID field.
Admin State: An 8-bit value representing the administrative state
of the radio. The following values are supported:
1 - Enabled
2 - Disabled
7.2.2. AC Name
The AC Name message element is defined in Section 5.2.3.
7.2.3. AC Name with Index
The AC Name with Index message element is sent by the AC to the WTP
to configure preferred ACs. The number of instances where this
message element would be present is equal to the number of ACs
configured on the WTP.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index | AC Name...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 90 for AC Name with Index
Length: 5
Index: The index of the preferred server (e.g., 1=primary,
2=secondary).
AC Name: A variable-length ASCII string containing the AC's name.
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7.2.4. WTP Board Data
The WTP Board Data message element is sent by the WTP to the AC and
contains information about the hardware present.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Card ID | Card Revision |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP Model |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP Model |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP Serial Number ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 50 for WTP Board Data
Length: 26
Card ID: A hardware identifier.
Card Revision: 4-byte Revision of the card.
WTP Model: 8-byte WTP Model Number.
WTP Serial Number: 24-byte WTP Serial Number.
Reserved: A 4-byte reserved field that MUST be set to zero (0).
Ethernet MAC Address: MAC address of the WTP's Ethernet interface.
7.2.5. Statistics Timer
The Statistics Timer message element value is used by the AC to
inform the WTP of the frequency that it expects to receive updated
statistics.
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Statistics Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 37 for Statistics Timer
Length: 2
Statistics Timer: A 16-bit unsigned integer indicating the time, in
seconds.
7.2.6. WTP Static IP Address Information
The WTP Static IP Address Information message element is used by an
AC to configure or clear a previously configured static IP address on
a WTP.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Netmask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Gateway |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Static |
+-+-+-+-+-+-+-+-+
Type: 82 for WTP Static IP Address Information
Length: 13
IP Address: The IP address to assign to the WTP.
Netmask: The IP Netmask.
Gateway: The IP address of the gateway.
Netmask: The IP Netmask.
Static: An 8-bit Boolean stating whether or not the WTP should use
a static IP address. A value of zero disables the static IP
address, while a value of one enables it.
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7.2.7. WTP Reboot Statistics
The WTP Reboot Statistics message element is sent by the WTP to the
AC to communicate information about reasons why reboots have
occurred.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Crash Count | LWAPP Initiated Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Failure Count | Failure Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 67 for WTP Reboot Statistics
Length: 7
Crash Count: The number of reboots that have occurred due to a WTP
crash.
LWAPP Initiated Count: The number of reboots that have occurred at
the request of some LWAPP message, such as a change in
configuration that required a reboot or an explicit LWAPP reset
request.
Link Failure Count: The number of times that an LWAPP connection
with an AC has failed.
Failure Type: The last WTP failure. The following values are
supported:
0 - Link Failure
1 - LWAPP Initiated
2 - WTP Crash
7.3. Configure Response
The Configure Response message is sent by an AC and provides an
opportunity for the AC to override a WTP's requested configuration.
Configure Responses are sent by an AC after receiving a Configure
Request.
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The Configure Response carries binding-specific message elements.
Refer to the appropriate binding for the definition of this
structure.
When a WTP receives a Configure Response, it acts upon the content of
the packet, as appropriate. If the Configure Response message
includes a Change State Event message element that causes a change in
the operational state of one of the Radios, the WTP will transmit a
Change State Event to the AC as an acknowledgement of the change in
state.
The following subsections define the message elements that MUST be
included in this LWAPP operation.
7.3.1. Decryption Error Report Period
The Decryption Error Report Period message element value is used by
the AC to inform the WTP of how frequently it should send decryption
error report messages.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Report Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 38 for Decryption Error Report Period
Length: 3
Radio ID: The Radio Identifier: typically refers to some interface
index on the WTP.
Report Interval: A 16-bit, unsigned integer indicating the time, in
seconds.
7.3.2. Change State Event
The WTP Radio Information message element is used to communicate the
operational state of a radio. The value contains two fields, as
shown.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | State | Cause |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 26 for Change State Event
Length: 3
Radio ID: The Radio Identifier: typically refers to some interface
index on the WTP.
State: An 8-bit Boolean value representing the state of the radio.
A value of one disables the radio, while a value of two enables
it.
Cause: In the event of a radio being inoperable, the Cause field
would contain the reason the radio is out of service. The
following values are supported:
0 - Normal
1 - Radio Failure
2 - Software Failure
7.3.3. LWAPP Timers
The LWAPP Timers message element is used by an AC to configure LWAPP
timers on a WTP.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discovery | Echo Request |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 68 for LWAPP Timers
Length: 2
Discovery: The number of seconds between LWAPP Discovery packets
when the WTP is in the discovery mode.
Echo Request: The number of seconds between WTP Echo Request LWAPP
messages.
7.3.4. AC IPv4 List
The AC List message element is defined in Section 6.2.6.
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7.3.5. AC IPv6 List
The AC List message element is defined in Section 6.2.7.
7.3.6. WTP Fallback
The WTP Fallback message element is sent by the AC to the WTP to
enable or disable automatic LWAPP fallback in the event that a WTP
detects its preferred AC, and is not currently connected to it.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Mode |
+-+-+-+-+-+-+-+-+
Type: 91 for WTP Fallback
Length: 1
Mode: The 8-bit Boolean value indicates the status of automatic
LWAPP fallback on the WTP. A value of zero disables the fallback
feature, while a value of one enables it. When enabled, if the
WTP detects that its primary AC is available, and it is not
connected to it, it SHOULD automatically disconnect from its
current AC and reconnect to its primary. If disabled, the WTP
will only reconnect to its primary through manual intervention
(e.g., through the Reset Request command).
7.3.7. Idle Timeout
The Idle Timeout message element is sent by the AC to the WTP to
provide it with the idle timeout that it should enforce on its active
mobile station entries.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timeout |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 97 for Idle Timeout
Length: 4
Timeout: The current idle timeout to be enforced by the WTP.
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7.4. Configuration Update Request
Configure Update Requests are sent by the AC to provision the WTP
while in the Run state. This is used to modify the configuration of
the WTP while it is operational.
When an AC receives a Configuration Update Request it will respond
with a Configuration Update Response, with the appropriate Result
Code.
The following subsections define the message elements introduced by
this LWAPP operation.
7.4.1. WTP Name
The WTP Name message element is defined in Section 6.1.3.
7.4.2. Change State Event
The Change State Event message element is defined in Section 7.3.2.
7.4.3. Administrative State
The Administrative State message element is defined in Section 7.2.1.
7.4.4. Statistics Timer
The Statistics Timer message element is defined in Section 7.2.5.
7.4.5. Location Data
The Location Data message element is defined in Section 6.1.4.
7.4.6. Decryption Error Report Period
The Decryption Error Report Period message element is defined in
Section 7.3.1.
7.4.7. AC IPv4 List
The AC List message element is defined in Section 6.2.6.
7.4.8. AC IPv6 List
The AC List message element is defined in Section 6.2.7.
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7.4.9. Add Blacklist Entry
The Add Blacklist Entry message element is used by an AC to add a
blacklist entry on a WTP, ensuring that the WTP no longer provides
any service to the MAC addresses provided in the message. The MAC
addresses provided in this message element are not expected to be
saved in non-volative memory on the WTP.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Num of Entries| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 65 for Add Blacklist Entry
Length: >= 7
Num of Entries: The number of MAC addresses in the array.
MAC Address: An array of MAC addresses to add to the blacklist
entry.
7.4.10. Delete Blacklist Entry
The Delete Blacklist Entry message element is used by an AC to delete
a previously added blacklist entry on a WTP, ensuring that the WTP
provides service to the MAC addresses provided in the message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Num of Entries| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 66 for Delete Blacklist Entry
Length: >= 7
Num of Entries: The number of MAC addresses in the array.
MAC Address: An array of MAC addresses to delete from the blacklist
entry.
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7.4.11. Add Static Blacklist Entry
The Add Static Blacklist Entry message element is used by an AC to
add a permanent Blacklist Entry on a WTP, ensuring that the WTP no
longer provides any service to the MAC addresses provided in the
message. The MAC addresses provided in this message element are
expected to be saved in non-volative memory on the WTP.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Num of Entries| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 70 for Delete Blacklist Entry
Length: >= 7
Num of Entries: The number of MAC addresses in the array.
MAC Address: An array of MAC addresses to add to the permanent
blacklist entry.
7.4.12. Delete Static Blacklist Entry
The Delete Static Blacklist Entry message element is used by an AC to
delete a previously added static blacklist entry on a WTP, ensuring
that the WTP provides service to the MAC addresses provided in the
message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Num of Entries| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 71 for Delete Blacklist Entry
Length: >= 7
Num of Entries: The number of MAC addresses in the array.
MAC Address: An array of MAC addresses to delete from the static
blacklist entry.
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7.4.13. LWAPP Timers
The LWAPP Timers message element is defined in Section 7.3.3.
7.4.14. AC Name with Index
The AC Name with Index message element is defined in Section 7.2.3.
7.4.15. WTP Fallback
The WTP Fallback message element is defined in Section 7.3.6.
7.4.16. Idle Timeout
The Idle Timeout message element is defined in Section 7.3.7.
7.5. Configuration Update Response
The Configuration Update Response is the acknowledgement message for
the Configuration Update Request.
Configuration Update Responses are sent by a WTP after receiving a
Configuration Update Request.
When an AC receives a Configure Update Response, the result code
indicates if the WTP successfully accepted the configuration.
The following subsections define the message elements that must be
present in this LWAPP operation.
7.5.1. Result Code
The Result Code message element is defined in Section 6.2.1.
7.6. Change State Event Request
The Change State Event is used by the WTP to inform the AC of a
change in the operational state.
The Change State Event message is sent by the WTP when it receives a
Configuration Response that includes a Change State Event message
element. It is also sent in the event that the WTP detects an
operational failure with a radio. The Change State Event may be sent
in either the Configure or Run state (see Figure 2).
When an AC receives a Change State Event it will respond with a
Change State Event Response and make any necessary modifications to
internal WTP data structures.
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The following subsections define the message elements that must be
present in this LWAPP operation.
7.6.1. Change State Event
The Change State Event message element is defined in Section 7.3.2.
7.7. Change State Event Response
The Change State Event Response acknowledges the Change State Event.
Change State Event Responses are sent by a WTP after receiving a
Change State Event.
The Change State Event Response carries no message elements. Its
purpose is to acknowledge the receipt of the Change State Event.
The WTP does not need to perform any special processing of the Change
State Event Response message.
7.8. Clear Config Indication
The Clear Config Indication is used to reset a WTP's configuration.
The Clear Config Indication is sent by an AC to request that a WTP
reset its configuration to manufacturing defaults. The Clear Config
Indication message is sent while in the Run LWAPP state.
The Reset Request carries no message elements.
When a WTP receives a Clear Config Indication, it will reset its
configuration to manufacturing defaults.
8. Device Management Operations
This section defines LWAPP operations responsible for debugging,
gathering statistics, logging, and firmware management.
8.1. Image Data Request
The Image Data Request is used to update firmware on the WTP. This
message and its companion response are used by the AC to ensure that
the image being run on each WTP is appropriate.
Image Data Requests are exchanged between the WTP and the AC to
download a new program image to a WTP.
When a WTP or AC receives an Image Data Request, it will respond with
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an Image Data Response.
The format of the Image Data and Image Download message elements are
described in the following subsections.
8.1.1. Image Download
The Image Download message element is sent by the WTP to the AC and
contains the image filename. The value is a variable-length byte
string. The string is NOT zero terminated.
8.1.2. Image Data
The Image Data message element is present when sent by the AC and
contains the following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode | Checksum | Image Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Image Data ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 33 for Image Data
Length: >= 5
Opcode: An 8-bit value representing the transfer opcode. The
following values are supported:
3 - Image Data is included.
5 - An error occurred. Transfer is aborted.
Checksum: A 16-bit value containing a checksum of the Image Data
that follows.
Image Data: The Image Data field contains 1024 characters, unless
the payload being sent is the last one (end of file).
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8.2. Image Data Response
The Image Data Response acknowledges the Image Data Request.
An Image Data Responses is sent in response to an Image Data Request.
Its purpose is to acknowledge the receipt of the Image Data Request
packet.
The Image Data Response carries no message elements.
No action is necessary on receipt.
8.3. Reset Request
The Reset Request is used to cause a WTP to reboot.
Reset Requests are sent by an AC to cause a WTP to reinitialize its
operation.
The Reset Request carries no message elements.
When a WTP receives a Reset Request it will respond with a Reset
Response and then reinitialize itself.
8.4. Reset Response
The Reset Response acknowledges the Reset Request.
Reset Responses are sent by a WTP after receiving a Reset Request.
The Reset Response carries no message elements. Its purpose is to
acknowledge the receipt of the Reset Request.
When an AC receives a Reset Response, it is notified that the WTP
will now reinitialize its operation.
8.5. WTP Event Request
The WTP Event Request is used by a WTP to send information to its AC.
These types of events may be periodical, or some asynchronous event
on the WTP. For instance, a WTP collects statistics and uses the WTP
Event Request to transmit this information to the AC.
When an AC receives a WTP Event Request, it will respond with a WTP
Event Request.
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The WTP Event Request message MUST contain one of the following
message element described in the next subsections, or a message
element that is defined for a specific technology.
8.5.1. Decryption Error Report
The Decryption Error Report message element value is used by the WTP
to inform the AC of decryption errors that have occurred since the
last report.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID |Num Of Entries | Mobile MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mobile MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 39 for Decryption Error Report
Length: >= 8
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP.
Num Of Entries: An 8-bit unsigned integer indicating the number of
mobile MAC addresses.
Mobile MAC Address: An array of mobile station MAC addresses that
have caused decryption errors.
8.5.2. Duplicate IPv4 Address
The Duplicate IPv4 Address message element is used by a WTP to inform
an AC that it has detected another host using the same IP address it
is currently using.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 77 for Duplicate IPv4 Address
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Length: 10
IP Address: The IP address currently used by the WTP.
MAC Address: The MAC address of the offending device.
8.5.3. Duplicate IPv6 Address
The Duplicate IPv6 Address message element is used by a WTP to inform
an AC that it has detected another host using the same IP address it
is currently using.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 77 for Duplicate IPv6 Address
Length: 10
IP Address: The IP address currently used by the WTP.
MAC Address: The MAC address of the offending device.
8.6. WTP Event Response
The WTP Event Response acknowledges the WTP Event Request.
WTP Event Responses are sent by an AC after receiving a WTP Event
Request.
The WTP Event Response carries no message elements.
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8.7. Data Transfer Request
The Data Transfer Request is used to upload debug information from
the WTP to the AC.
Data Transfer Requests are sent by the WTP to the AC when it
determines that it has important information to send to the AC. For
instance, if the WTP detects that its previous reboot was caused by a
system crash, it would want to send the crash file to the AC. The
remote debugger function in the WTP also uses the Data Transfer
Request in order to send console output to the AC for debugging
purposes.
When an AC receives a Data Transfer Request, it will respond with a
Data Transfer Response. The AC may log the information received as
it sees fit.
The Data Transfer Request message MUST contain ONE of the following
message element described in the next subsection.
8.7.1. Data Transfer Mode
The Data Transfer Mode message element is used by the AC to request
information from the WTP for debugging purposes.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Data Type |
+-+-+-+-+-+-+-+-+
Type: 52 for Data Transfer Mode
Length: 1
Data Type: An 8-bit value describing the type of information being
requested. The following values are supported:
1 - WTP Crash Data
2 - WTP Memory Dump
8.7.2. Data Transfer Data
The Data Transfer Data message element is used by the WTP to provide
information to the AC for debugging purposes.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Type | Data Length | Data ....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 53 for Data Transfer Data
Length: >= 3
Data Type: An 8-bit value describing the type of information being
sent. The following values are supported:
1 - WTP Crash Data
2 - WTP Memory Dump
Data Length: Length of data field.
Data: Debug information.
8.8. Data Transfer Response
The Data Transfer Response acknowledges the Data Transfer Request.
A Data Transfer Response is sent in response to a Data Transfer
Request. Its purpose is to acknowledge the receipt of the Data
Transfer Request packet.
The Data Transfer Response carries no message elements.
Upon receipt of a Data Transfer Response, the WTP transmits more
information, if any is available.
9. Mobile Session Management
Messages in this section are used by the AC to create, modify, or
delete mobile station session state on the WTPs.
9.1. Mobile Config Request
The Mobile Config Request message is used to create, modify, or
delete mobile session state on a WTP. The message is sent by the AC
to the WTP, and may contain one or more message elements. The
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message elements for this LWAPP control message include information
that is generally highly technology-specific. Therefore, please
refer to the appropriate binding section or document for the
definitions of the messages elements that may be used in this control
message.
This section defines the format of the Delete Mobile message element,
since it does not contain any technology-specific information.
9.1.1. Delete Mobile
The Delete Mobile message element is used by the AC to inform a WTP
that it should no longer provide service to a particular mobile
station. The WTP must terminate service immediately upon receiving
this message element.
The transmission of a Delete Mobile message element could occur for
various reasons, including administrative reasons, as a result of the
fact that the mobile has roamed to another WTP, etc.
Once access has been terminated for a given station, any future
packets received from the mobile must result in a deauthenticate
message, as specified in [6].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 30 for Delete Mobile
Length: 7
Radio ID: An 8-bit value representing the radio
MAC Address: The mobile station's MAC address
9.2. Mobile Config Response
The Mobile Configuration Response is used to acknowledge a previously
received Mobile Configuration Request, and includes a Result Code
message element that indicates whether an error occurred on the WTP.
This message requires no special processing and is only used to
acknowledge the Mobile Configuration Request.
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The Data Transfer Request message MUST contain the message elements
described in the next subsection.
9.2.1. Result Code
The Result Code message element is defined in Section 6.2.1.
10. LWAPP Security
Note: This version only defines a certificate and a shared-secret-
based mechanism to secure control LWAPP traffic exchanged between the
WTP and the AC.
10.1. Securing WTP-AC Communications
While it is generally straightforward to produce network
installations in which the communications medium between the WTP and
AC is not accessible to the casual user (e.g., these LAN segments are
isolated, and no RJ45 or other access ports exist between the WTP and
the AC), this will not always be the case. Furthermore, a determined
attacker may resort to various, more sophisticated monitoring and/or
access techniques, thereby compromising the integrity of this
connection.
In general, a certain level of threat on the local (wired) LAN is
expected and accepted in most computing environments. That is, it is
expected that in order to provide users with an acceptable level of
service and maintain reasonable productivity levels, a certain amount
of risk must be tolerated. It is generally believed that a certain
perimeter is maintained around such LANs, that an attacker must have
access to the building(s) in which such LANs exist, and that they
must be able to "plug in" to the LAN in order to access the network.
With these things in mind, we can begin to assess the general
security requirements for AC-WTP communications. While an in-depth
security analysis of threats and risks to these communications is
beyond the scope of this document, some discussion of the motivation
for various security-related design choices is useful. The
assumptions driving the security design thus far include the
following:
o WTP-AC communications take place over a wired connection that may
be accessible to a sophisticated attacker.
o access to this connection is not trivial for an outsider (i.e.,
someone who does not "belong" in the building) to access.
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o if authentication and/or privacy of end-to-end traffic for which
the WTP and AC are intermediaries is required, this may be
provided via IPsec [14].
o privacy and authentication for at least some WTP-AC control
traffic is required (e.g., Wired Equivalent Privacy (WEP) keys for
user sessions, passed from the AC to the WTP).
o the AC can be trusted to generate strong cryptographic keys.
The AC-WTP traffic can be considered to consist of two types: data
traffic (e.g., to or from an end user), and control traffic, which is
strictly between the AC and WTP. Since data traffic may be secured
using IPsec (or some other end-to-end security mechanism), we confine
our solution to control traffic. The resulting security consists of
two components: an authenticated key exchange and control traffic
security encapsulation. The security encapsulation is accomplished
using AES-CCM, described in [3]. This encapsulation provides for
strong AES-based authentication and encryption [2]. The exchange of
cryptographic keys used for CCM is described below.
10.2. LWAPP Frame Encryption
While the LWAPP protocol uses AES-CCM to encrypt control traffic, it
is important to note that not all control frames are encrypted. The
LWAPP discovery and join phase are not encrypted. The Discovery
messages are sent in the clear since there does not exist a security
association between the WTP and the AC during the discovery phase.
The join phase is an authenticated exchange used to negotiate
symmetric session keys (see Section 10.3).
Once the join phase has been successfully completed, the LWAPP state
machine Figure 2 will move to the Configure state, at which time all
LWAPP control frames are encrypted using AES-CCM.
Encryption of a control message begins at the Message Element field:
meaning the Msg Type, Seq Num, Msg Element Length, and Session ID
fields are left intact (see Section 4.2.1).
The AES-CCM 12-byte authentication data is appended to the end of the
message. The authentication data is calculated from the start of the
LWAPP packet and includes the complete LWAPP control header (see
Section 4.2.1).
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The AES-CCM block cipher protocol requires an initialization vector.
The LWAPP protocol requires that the WTP and the AC maintain two
separate IVs, one for transmission and one for reception. The IV
derived during the key exchange phase by both the WTP and the AC is
used as the base for all encrypted packets with a new key.
10.3. Authenticated Key Exchange
This section describes the key management component of the LWAPP
protocol. There are two modes supported by LWAPP: certificate and
pre-shared key.
10.3.1. Terminology
This section details the key management protocol that makes use of
pre-shared secrets.
The following notations are used throughout this section:
o PSK - the pre-shared key shared between the WTP and the AC.
o Kpriv - the private key of a public-private key pair.
o Kpub - the public key of the pair.
o SessionID - a randomly generated LWAPP session identifier,
provided by the WTP in the Join Request.
o E-x{Kpub, M} - RSA encryption of M using X's public key.
o D-x{Kpriv, C} - RSA decryption of C using X's private key.
o AES-CMAC(key, packet) - A message integrity check, using AES-CMAC
and key, of the complete LWAPP packet, with the Sequence Number
field and the payload of the PSK-MIC message element set to zero.
o AES-E(key, plaintext) - Plaintext is encrypted with key, using
AES.
o AES-D(key, ciphertext) - ciphertext is decrypted with key, using
AES.
o Certificate-AC - AC's Certificate.
o Certificate-WTP - WTP's Certificate.
o WTP-MAC - The WTP's MAC address.
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o AC-MAC - The AC's MAC address.
o RK0 - the root key, which is created through a Key Derivation
Function (KDF) function.
o RK0E - the root Encryption key, derived from RK0.
o RK0M - the root MIC key, derived from RK0.
o SK1 - the session key.
o SK1C - the session confirmation key, derived from SK.
o SK1E - the session encryption key, derived from SK.
o SK1W - the session keywrap key, derived from SK (see RFC 3394
[9]).
o WNonce - The WTP's randomly generated nonce.
o ANonce - The AC's randomly generated nonce.
o EWNonce - The payload of the WNonce message element, which
includes the WNonce.
o EANonce - The payload of the ANonce message element, which
includes the ANonce.
10.3.2. Initial Key Generation
The AC and WTP accomplish mutual authentication and a cryptographic
key exchange in a dual round trip using the Join Request, Join
Response, Join ACK, and Join Confirm (see Section 6.1).
The following text describes the exchange between the WTP and the AC
that creates a session key, which is used to secure LWAPP control
messages.
o The WTP creates a Join Request using the following process:
o If certificate-based security is used, the WTP adds the
Certificate message element (see Section 6.1.6) with its
contents set to Certificate-WTP.
o The WTP adds the Session ID message element (see Section 6.1.7)
with the contents set to a randomly generated session
identifier (see RFC 1750 [4]). The WTP MUST save the Session
ID in order to validate the Join Response.
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o The WTP creates a random nonce, included in the XNonce message
element (see Section 6.1.9). The WTP MUST save the XNonce to
validate the Join Response.
o The WTP transmits the Join Request to the AC.
o Upon receiving the Join Request, the AC uses the following
process:
o The AC creates the Join Response, and ensures that the Session
ID message element matches the value found in the Join Request.
o If certificate-based security is used, the AC:
o adds the Certificate-AC to the Certificate message element.
o creates a random 'AC Nonce' and encrypts it using the
following algorithm E-wtp(Kpub, XNonce XOR 'AC Nonce'). The
encrypted contents are added to the ANonce's message element
payload.
o If a pre-shared-key-based security is used, the AC:
o creates RK0 through the following algorithm: RK0 = KDF-
256{PSK, "LWAPP PSK Top K0" || Session ID || WTP-MAC || AC-
MAC}, where WTP-MAC is the WTP's MAC address in the form
"xx:xx:xx:xx:xx:xx". Similarly, the AC-MAC is an ASCII
encoding of the AC's MAC address, of the form "xx:xx:xx:xx:
xx:xx". The resulting K0 is split into the following:
o The first 16 octets are known as RK0E, and are used as an
encryption key.
o The second 16 octets are known as RK0M, and are used for
MIC'ing purposes.
o The AC creates a random 'AC Nonce' and encrypts it using the
following algorithm: AES-E(RK0E, XNonce XOR 'AC Nonce').
The encrypted contents are added to the ANonce's message
element payload.
o The AC adds a MIC to the contents of the Join Response using
AES-CMAC(RK0M, Join Response) and adds the resulting hash to
the PSK-MIC (Section 6.2.9) message element.
o Upon receiving the Join Response, the WTP uses the following
process:
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o If a pre-shared key is used, the WTP authenticates the Join
Response's PSK-MIC message element. If authentication fails,
the packet is dropped.
o The WTP decrypts the ANonce message element and XOR's the value
with XNonce to retrieve the 'AC Nonce'. The ANonce payload is
referred to as ciphertext below:
o If a pre-shared key is used, use AES-D(RK0E, ciphertext).
The 'AC Nonce' is then recovered using XNonce XOR plaintext.
o If certificates are used, use d-wtp(Kpriv, ciphertext). The
'AC Nonce' is then recovered using XNonce XOR plaintext.
o The WTP creates a random 'WTP Nonce'.
o The WTP uses the KDF function to create a 64-octet session key
(SK). The KDF function used is as follows: KDF-512{'WTP Nonce'
|| 'AC Nonce', "LWAPP Key Generation", WTP-MAC || AC-MAC}. The
KDF function is defined in [7].
o SK is then broken down into three separate session keys with
different purposes:
o The first 16 octets are known as SK1C, and are used as a
confirmation key.
o The second 16 octets are known as SK1E, and are as the
encryption key.
o The third 16 octets are known as SK1D, and are used as the
keywrap key.
o The fourth 16 octets are known as IV, and are used as the
Initialization Vector during encryption.
o The WTP creates the Join ACK message.
o If certificate-based security is used, the AC:
o encrypts the 'WTP Nonce' using the following algorithm: E-
ac(Kpub, 'WTP Nonce'). The encrypted contents are added to
the WNonce's message element payload.
o If a pre-shared-key-based security is used, the AC:
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o encrypts the 'WTP Nonce' using the following algorithm:
AES-E(RK0E, 'WTP Nonce'). The encrypted contents are added
to the WNonce's message element payload.
o The WTP adds a MIC to the contents of the Join ACK using
AES-CMAC(SK1M, Join ACK) and adds the resulting hash to the
PSK-MIC (Section 6.2.9) message element.
o The WTP then transmits the Join ACK to the AC.
o Upon receiving the Join ACK, the AC uses the following process:
o The AC authenticates the Join ACK through the PSK-MIC message
element. If authentic, the AC decrypts the WNonce message
element to retrieve the 'WTP Nonce'. If the Join ACK cannot be
authenticated, the packet is dropped.
o The AC decrypts the WNonce message element to retrieve the 'WTP
Nonce'. The WNonce payload is referred to as ciphertext below:
o If a pre-shared key is used, use AES-D(RK0E, ciphertext).
The plaintext is then considered the 'WTP Nonce'.
o If certificates are used, use d-ac(Kpriv, ciphertext). The
plaintext is then considered the 'WTP Nonce'.
o The AC then uses the KDF function to create a 64-octet session
key (SK). The KDF function used is as follows: KDF-512{'WTP
Nonce' || 'AC Nonce', "LWAPP Key Generation", WTP-MAC ||
AC-MAC}. The KDF function is defined in [7]. The SK is split
into SK1C, SK1E, SK1D, and IV, as previously noted.
o The AC creates the Join Confirm.
o The AC adds a MIC to the contents of the Join Confirm using
AES-CMAC(SK1M, Join Confirm) and adds the resulting hash to the
MIC (Section 6.2.9) message element.
o The AC then transmits the Join Confirm to the WTP.
o Upon receiving the Join Confirm, the WTP uses the following
process:
o The WTP authenticates the Join Confirm through the PSK-MIC
message element. If the Join Confirm cannot be authenticated,
the packet is dropped.
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o SK1E is now plumbed into the AC and WTP's crypto engine as the
AES-CCM LWAPP control encryption session key. Furthermore, the
random IV is used as the base Initialization Vector. From this
point on, all control protocol payloads between the WTP and AC are
encrypted and authenticated using the new session key.
10.3.3. Refreshing Cryptographic Keys
Since AC-WTP associations will tend to be relatively long-lived, it
is sensible to periodically refresh the encryption and authentication
keys; this is referred to as "rekeying". When the key lifetime
reaches 95% of the configured value, identified in the KeyLifetime
timer (see Section 12), the rekeying will proceed as follows:
o The WTP creates RK0 through the previously defined KDF algorithm:
RK0 = KDF-256{SK1D, "LWAPP PSK Top K0" || Session ID || WTP-MAC ||
AC-MAC}. Note that the difference in this specific instance is
that SK1D that was previously generated is used instead of the
PSK. Note this is used in both the certificate and pre-shared key
modes. The resulting RK0 creates RK0E, RK0M.
o The remaining steps used are identical to the join process, with
the exception that the rekey messages are used instead of join
messages, and the fact that the messages are encrypted using the
previously created SK1E. This means the Join Request is replaced
with the Rekey Request, the Join Response is replaced with the
Rekey Response, etc. The two differences between the rekey and
the join process are:
o The Certificate-WTP and Certificate-AC are not included in the
Rekey-Request and Rekey-Response, respectively.
o Regardless of whether certificates or pre-shared keys were used
in the initial key derivation, the process now uses the pre-
shared key mode only, using SK1D as the "PSK".
o The Key Update Request is sent to the AC.
o The newly created SK1E is now plumbed into the AC and WTP's crypto
engine as the AES-CCM LWAPP control encryption session key.
Furthermore, the new random IV is used as the base Initialization
Vector. From this point on, all control protocol payloads between
the WTP and AC are encrypted and authenticated using the new
session key.
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If either the WTP or the AC do not receive an expected response by
the time the ResponseTimeout timer expires (see Section 12), the
WTP MUST delete the new and old session information, and reset the
state machine to the Idle state.
Following a rekey process, both the WTP and the AC keep the
previous encryption for 5-10 seconds in order to be able to
process packets that arrive out of order.
10.4. Certificate Usage
Validation of the certificates by the AC and WTP is required so that
only an AC may perform the functions of an AC and that only a WTP may
perform the functions of a WTP. This restriction of functions to the
AC or WTP requires that the certificates used by the AC MUST be
distinguishable from the certificate used by the WTP. To accomplish
this differentiation, the x.509v3 certificates MUST include the
Extensions field [10] and MUST include the NetscapeComment [11]
extension.
For an AC, the value of the NetscapeComment extension MUST be the
string "CAPWAP AC Device Certificate". For a WTP, the value of the
NetscapeComment extension MUST be the string "CAPWAP WTP Device
Certificate".
Part of the LWAPP certificate validation process includes ensuring
that the proper string is included in the NetscapeComment extension,
and only allowing the LWAPP session to be established if the
extension does not represent the same role as the device validating
the certificate. For instance, a WTP MUST NOT accept a certificate
whose NetscapeComment field is set to "CAPWAP WTP Device
Certificate".
11. IEEE 802.11 Binding
This section defines the extensions required for the LWAPP protocol
to be used with the IEEE 802.11 protocol.
11.1. Division of Labor
The LWAPP protocol, when used with IEEE 802.11 devices, requires a
specific behavior from the WTP and the AC, specifically in terms of
which 802.11 protocol functions are handled.
For both the Split and Local MAC approaches, the CAPWAP functions, as
defined in the taxonomy specification, reside in the AC.
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11.1.1. Split MAC
This section shows the division of labor between the WTP and the AC
in a Split MAC architecture. Figure 3 shows the clear separation of
functionality among LWAPP components.
Function Location
Distribution Service AC
Integration Service AC
Beacon Generation WTP
Probe Response WTP
Power Mgmt/Packet Buffering WTP
Fragmentation/Defragmentation WTP
Assoc/Disassoc/Reassoc AC
802.11e
Classifying AC
Scheduling WTP/AC
Queuing WTP
802.11i
802.1X/EAP AC
Key Management AC
802.11 Encryption/Decryption WTP or AC
Figure 3: Mapping of 802.11 Functions for Split MAC Architecture
The Distribution and Integration services reside on the AC, and
therefore all user data is tunneled between the WTP and the AC. As
noted above, all real-time 802.11 services, including the control
protocol and the beacon and Probe Response frames, are handled on the
WTP.
All remaining 802.11 MAC management frames are supported on the AC,
including the Association Request, which allows the AC to be involved
in the access policy enforcement portion of the 802.11 protocol. The
802.1X and 802.11i key management function are also located on the
AC.
While the admission control component of 802.11e resides on the AC,
the real-time scheduling and queuing functions are on the WTP. Note
that this does not exclude the AC from providing additional policing
and scheduling functionality.
Note that in the following figure, the use of '( - )' indicates that
processing of the frames is done on the WTP.
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Client WTP AC
Beacon
<-----------------------------
Probe Request
----------------------------( - )------------------------->
Probe Response
<-----------------------------
802.11 AUTH/Association
<--------------------------------------------------------->
Add Mobile (Clear Text, 802.1X Only)
<------------------------->
802.1X Authentication & 802.11i Key Exchange
<--------------------------------------------------------->
Add Mobile (AES-CCMP, PTK=x)
<------------------------->
802.11 Action Frames
<--------------------------------------------------------->
802.11 DATA (1)
<---------------------------( - )------------------------->
Figure 4: Split MAC Message Flow
Figure 4 provides an illustration of the division of labor in a Split
MAC architecture. In this example, a WLAN has been created that is
configured for 802.11i, using AES-CCMP for privacy. The following
process occurs:
o The WTP generates the 802.11 beacon frames, using information
provided to it through the Add WLAN (see Section 11.8.1.1) message
element.
o The WTP processes the Probe Request and responds with a
corresponding Probe Response. The problem request is then
forwarded to the AC for optional processing.
o The WTP forwards the 802.11 Authentication and Association frames
to the AC, which is responsible for responding to the client.
o Once the association is complete, the AC transmits an LWAPP Add
Mobile Request to the WTP (see Section 11.7.1.1). In the above
example, the WLAN is configured for 802.1X, and therefore the
'802.1X only' policy bit is enabled.
o If the WTP is providing encryption/decryption services, once the
client has completed the 802.11i key exchange, the AC transmits
another Add Mobile Request to the WTP, stating the security policy
to enforce for the client (in this case AES-CCMP), as well as the
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encryption key to use. If encryption/decryption is handled in the
AC, the Add Mobile Request would have the encryption policy set to
"Clear Text".
o The WTP forwards any 802.11 Action frames received to the AC.
o All client data frames are tunneled between the WTP and the AC.
Note that the WTP is responsible for encrypting and decrypting
frames, if it was indicated in the Add Mobile Request.
11.1.2. Local MAC
This section shows the division of labor between the WTP and the AC
in a Local MAC architecture. Figure 5 shows the clear separation of
functionality among LWAPP components.
Function Location
Distribution Service WTP
Integration Service WTP
Beacon Generation WTP
Probe Response WTP
Power Mgmt/Packet Buffering WTP
Fragmentation/Defragmentation WTP
Assoc/Disassoc/Reassoc WTP
802.11e
Classifying WTP
Scheduling WTP
Queuing WTP
802.11i
802.1X/EAP AC
Key Management AC
802.11 Encryption/Decryption WTP
Figure 5: Mapping of 802.11 Functions for Local AP Architecture
Given that Distribution and Integration Services exist on the WTP,
client data frames are not forwarded to the AC, with the exception
listed in the following paragraphs.
While the MAC is terminated on the WTP, it is necessary for the AC to
be aware of mobility events within the WTPs. As a consequence, the
WTP MUST forward the 802.11 Association Requests to the AC, and the
AC MAY reply with a failed Association Response if it deems it
necessary.
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The 802.1X and 802.11i Key Management function resides in the AC.
Therefore, the WTP MUST forward all 802.1X/Key Management frames to
the AC and forward the associated responses to the station.
Note that in the following figure, the use of '( - )' indicates that
processing of the frames is done on the WTP.
Client WTP AC
Beacon
<-----------------------------
Probe
<---------------------------->
802.11 AUTH
<-----------------------------
802.11 Association
<---------------------------( - )------------------------->
Add Mobile (Clear Text, 802.1X Only)
<------------------------->
802.1X Authentication & 802.11i Key Exchange
<--------------------------------------------------------->
802.11 Action Frames
<--------------------------------------------------------->
Add Mobile (AES-CCMP, PTK=x)
<------------------------->
802.11 DATA
<----------------------------->
Figure 6: Local MAC Message Flow
Figure 6 provides an illustration of the division of labor in a Local
MAC architecture. In this example, a WLAN has been created that is
configured for 802.11i, using AES-CCMP for privacy. The following
process occurs:
o The WTP generates the 802.11 beacon frames, using information
provided to it through the Add WLAN (see Section 11.8.1.1) message
element.
o The WTP processes the Probe Request and responds with a
corresponding Probe Response.
o The WTP forwards the 802.11 Authentication and Association frames
to the AC, which is responsible for responding to the client.
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o Once the association is complete, the AC transmits an LWAPP Add
Mobile Request to the WTP (see Section 11.7.1.1. In the above
example, the WLAN is configured for 802.1X, and therefore the
'802.1X only' policy bit is enabled.
o The WTP forwards all 802.1X and 802.11i key exchange messages to
the AC for processing.
o The AC transmits another Add Mobile Request to the WTP, stating
the security policy to enforce for the client (in this case, AES-
CCMP), as well as the encryption key to use. The Add Mobile
Request MAY include a VLAN name, which when present is used by the
WTP to identify the VLAN on which the user's data frames are to be
bridged.
o The WTP forwards any 802.11 Action frames received to the AC.
o The WTP locally bridges all client data frames, and provides the
necessary encryption and decryption services.
11.2. Roaming Behavior and 802.11 Security
It is important that LWAPP implementations react properly to mobile
devices associating to the networks in how they generate Add Mobile
and Delete Mobile messages. This section expands upon the examples
provided in the previous section, and describes how the LWAPP control
protocol is used in order to provide secure roaming.
Once a client has successfully associated with the network in a
secure fashion, it is likely to attempt to roam to another access
point. Figure 7 shows an example of a currently associated station
moving from its "Old WTP" to a new "WTP". The figure is useful for
multiple different security policies, including standard 802.1X and
dynamic WEP keys, WPA or even WPA2 both with key caching (where the
802.1x exchange would be bypassed) and without.
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Client Old WTP WTP AC
Association Request/Response
<--------------------------------------( - )-------------->
Add Mobile (Clear Text, 802.1X Only)
<---------------->
802.1X Authentication (if no key cache entry exists)
<--------------------------------------( - )-------------->
802.11i 4-way Key Exchange
<--------------------------------------( - )-------------->
Delete Mobile
<---------------------------------->
Add Mobile (AES-CCMP, PTK=x)
<---------------->
Figure 7: Client Roaming Example
11.3. Transport-Specific Bindings
All LWAPP transports have the following IEEE 802.11 specific
bindings:
11.3.1. Status and WLANS Field
The interpretation of this 16-bit field depends on the direction of
transmission of the packet. Refer to the figure in Section 3.1.
Status
When an LWAPP packet is transmitted from a WTP to an AC, this field
is called the Status field and indicates radio resource information
associated with the frame. When the message is an LWAPP control
message this field is transmitted as zero.
The Status field is divided into the signal strength and signal-to-
noise ratio with which an IEEE 802.11 frame was received, encoded in
the following manner:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RSSI | SNR |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
RSSI: RSSI is a signed, 8-bit value. It is the received signal
strength indication, in dBm.
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SNR: SNR is a signed, 8-bit value. It is the signal-to-noise ratio
of the received IEEE 802.11 frame, in dB.
WLANs field: When an LWAPP data message is transmitted from an AC
to a WTP, this 16-bit field indicates on which WLANs the
encapsulated IEEE 802.11 frame is to be transmitted. For unicast
packets, this field is not used by the WTP. For broadcast or
multicast packets, the WTP might require this information if it
provides encryption services.
Given that a single broadcast or multicast packet might need to be
sent to multiple wireless LANs (presumably each with a different
broadcast key), this field is defined as a bit field. A bit set
indicates a WLAN ID (see Section 11.8.1.1), which will be sent the
data. The WLANS field is encoded in the following manner:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WLAN ID(s) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
11.4. BSSID to WLAN ID Mapping
The LWAPP protocol makes assumptions regarding the BSSIDs used on the
WTP. It is a requirement for the WTP to use a contiguous block of
BSSIDs. The WLAN Identifier field, which is managed by the AC, is
used as an offset into the BSSID list.
For instance, if a WTP had a base BSSID address of 00:01:02:00:00:00,
and the AC sent an Add WLAN message with a WLAN Identifier of 2 (see
Section 11.8.1.1), the BSSID for the specific WLAN on the WTP would
be 00:01:02:00:00:02.
The WTP communicates the maximum number of BSSIDs that it supports
during the Config Request within the IEEE 802.11 WTP WLAN Radio
Configuration message element (see Section 11.9.1).
11.5. Quality of Service
It is recommended that 802.11 MAC management be sent by both the AC
and the WTP with appropriate Quality-of-Service (QoS) values,
ensuring that congestion in the network minimizes occurrences of
packet loss. Therefore, a QoS-enabled LWAPP device should use:
802.1P: The precedence value of 6 SHOULD be used for all 802.11 MAC
management messages, except for Probe Requests, which SHOULD use
4.
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DSCP: The DSCP tag value of 46 SHOULD be used for all 802.11 MAC
management messages, except for Probe Requests, which SHOULD use
34.
11.6. Data Message Bindings
There are no LWAPP data message bindings for IEEE 802.11.
11.7. Control Message Bindings
The IEEE 802.11 binding has the following control message
definitions.
11.7.1. Mobile Config Request
This section contains the 802.11-specific message elements that are
used with the Mobile Config Request.
11.7.1.1. Add Mobile
The Add Mobile Request is used by the AC to inform a WTP that it
should forward traffic from a particular mobile station. The Add
Mobile Request may also include security parameters that must be
enforced by the WTP for the particular mobile.
When the AC sends an Add Mobile Request, it includes any security
parameters that may be required. An AC that wishes to update a
mobile's policy on a WTP may do so by simply sending a new Add Mobile
message element.
When a WTP receives an Add Mobile message element, it must first
override any existing state it may have for the mobile station in
question. The latest Add Mobile overrides any previously received
messages. If the Add Mobile message element's EAP-Only bit is set,
the WTP MUST drop all 802.11 packets that do not contain EAP packets.
Note that when EAP Only is set, the Encryption Policy field MAY have
additional values, and therefore it is possible to inform a WTP to
only accept encrypted EAP packets. Once the mobile station has
successfully completed EAP authentication, the AC must send a new Add
Mobile message element to push the session key down to the WTP as
well as to remove the EAP Only restriction.
If the QoS field is set, the WTP MUST observe and provide policing of
the 802.11e priority tag to ensure that it does not exceed the value
provided by the AC.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Association ID | MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |E|C| Encryption Policy |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Encrypt Policy | Session Key... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pairwise TSC... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pairwise RSC... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Capabilities | WLAN ID | WME Mode |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 802.11e Mode | Qos | Supported Rates |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Supported Rates |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VLAN Name...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 29 for Add Mobile
Length: 36
Radio ID: An 8-bit value representing the radio.
Association ID: A 16-bit value specifying the 802.11 Association
Identifier.
MAC Address: The mobile station's MAC address.
E: The 1-bit field is set by the AC to inform the WTP that it MUST
NOT accept any 802.11 data frames, other than 802.1X frames. This
is the equivalent of the WTP's 802.1X port for the mobile station
to be in the closed state. When set, the WTP MUST drop any
non-802.1X packets it receives from the mobile station.
C: The 1-bit field is set by the AC to inform the WTP that
encryption services will be provided by the AC. When set, the WTP
SHOULD police frames received from stations to ensure that they
comply to the stated encryption policy, but does not need to take
specific cryptographic action on the frame. Similarly, for
transmitted frames, the WTP only needs to forward already
encrypted frames.
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Encryption Policy: The policy field informs the WTP how to handle
packets from/to the mobile station. The following values are
supported:
0 - Encrypt WEP 104: All packets to/from the mobile station must
be encrypted using a standard 104-bit WEP.
1 - Clear Text: All packets to/from the mobile station do not
require any additional crypto processing by the WTP.
2 - Encrypt WEP 40: All packets to/from the mobile station must
be encrypted using a standard 40-bit WEP.
3 - Encrypt WEP 128: All packets to/from the mobile station must
be encrypted using a standard 128-bit WEP.
4 - Encrypt AES-CCMP 128: All packets to/from the mobile station
must be encrypted using a 128-bit AES-CCMP [7].
5 - Encrypt TKIP-MIC: All packets to/from the mobile station must
be encrypted using Temporal Key Integrity Protocol (TKIP) and
authenticated using Michael [16].
Session Key: A 32-octet session key the WTP is to use when
encrypting traffic to or decrypting traffic from the mobile
station. The type of key is determined based on the Encryption
Policy field.
Pairwise TSC: The TKIP Sequence Counter (TSC) to use for unicast
packets transmitted to the mobile.
Pairwise RSC: The Receive Sequence Counter (RSC) to use for unicast
packets received from the mobile.
Capabilities: A 16-bit field containing the 802.11 capabilities to
use with the mobile.
WLAN ID: An 8-bit value specifying the WLAN Identifier.
WME Mode: An 8-bit Boolean used to identify whether the station is
WME capable. A value of zero is used to indicate that the station
is not Wireless Multimedia Extension (WME) capable, while a value
of one means that the station is WME capable.
802.11e Mode: An 8-bit Boolean used to identify whether the station
is 802.11e-capable. A value of zero is used to indicate that the
station is not 802.11e-capable, while a value of one means that
the station is 802.11e-capable.
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QoS: An 8-bit value specifying the QoS policy to enforce for the
station. The following values are supported: PRC: TO CHECK
0 - Silver (Best Effort)
1 - Gold (Video)
2 - Platinum (Voice)
3 - Bronze (Background)
Supported Rates: The supported rates to be used with the mobile
station.
VLAN Name: An optional variable string containing the VLAN Name on
which the WTP is to locally bridge user data. Note that this
field is only valid with Local MAC WTPs.
11.7.1.2. IEEE 802.11 Mobile Session Key
The Mobile Session Key Payload message element is sent when the AC
determines that encryption of a mobile station must be performed in
the WTP. This message element MUST NOT be present without the Add
Mobile message element, and MUST NOT be sent if the WTP had not
specifically advertised support for the requested encryption scheme
(see Section 11.7.1.1).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address | Encryption Policy |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encryption Policy | Session Key... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 105 for IEEE 802.11 Mobile Session Key
Length: >= 11
MAC Address: The mobile station's MAC address.
Encryption Policy: The policy field informs the WTP how to handle
packets from/to the mobile station. The following values are
supported:
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0 - Encrypt WEP 104: All packets to/from the mobile station must
be encrypted using a standard 104-bit WEP.
1 - Clear Text: All packets to/from the mobile station do not
require any additional crypto processing by the WTP.
2 - Encrypt WEP 40: All packets to/from the mobile station must
be encrypted using a standard 40-bit WEP.
3 - Encrypt WEP 128: All packets to/from the mobile station must
be encrypted using a standard 128-bit WEP.
4 - Encrypt AES-CCMP 128: All packets to/from the mobile station
must be encrypted using a 128-bit AES-CCMP [7].
5 - Encrypt TKIP-MIC: All packets to/from the mobile station must
be encrypted using TKIP and authenticated using Michael [16].
Session Key: The session key the WTP is to use when encrypting
traffic to/from the mobile station.
11.7.1.3. Station QoS Profile
The Station QoS Profile Payload message element contains the maximum
802.11e priority tag that may be used by the station. Any packets
received that exceed the value encoded in this message element must
either be dropped or tagged using the maximum value permitted to the
user. The priority tag must be between zero (0) and seven (7).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address | 802.1P Precedence Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 140 for IEEE 802.11 Station QoS Profile
Length: 12
MAC Address: The mobile station's MAC address.
802.1P Precedence Tag: The maximum 802.1P precedence value that the
WTP will allow in the Traffic Identifier (TID) field in the
extended 802.11e QoS Data header.
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11.7.1.4. IEEE 802.11 Update Mobile QoS
The Update Mobile QoS message element is used to change the Quality-
of-Service policy on the WTP for a given mobile station.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Association ID | MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address | QoS Profile | Vlan Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DSCP Tag | 802.1P Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 106 for IEEE 802.11 Update Mobile QoS
Length: 14
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP.
Association ID: The 802.11 Association Identifier.
MAC Address: The mobile station's MAC address.
QoS Profile: An 8-bit value specifying the QoS policy to enforce
for the station. The following values are supported:
0 - Silver (Best Effort)
1 - Gold (Video)
2 - Platinum (Voice)
3 - Bronze (Background)
VLAN Identifier: PRC.
DSCP Tag: The DSCP label to use if packets are to be DSCP tagged.
802.1P Tag: The 802.1P precedence value to use if packets are to be
802.1P-tagged.
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11.7.2. WTP Event Request
This section contains the 802.11-specific message elements that are
used with the WTP Event Request message.
11.7.2.1. IEEE 802.11 Statistics
The Statistics message element is sent by the WTP to transmit its
current statistics. The value contains the following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Tx Fragment Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Tx Fragment Cnt| Multicast Tx Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mcast Tx Cnt | Failed Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Failed Count | Retry Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retry Count | Multiple Retry Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Multi Retry Cnt| Frame Duplicate Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame Dup Cnt | RTS Success Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RTS Success Cnt| RTS Failure Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RTS Failure Cnt| ACK Failure Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|ACK Failure Cnt| Rx Fragment Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Rx Fragment Cnt| Multicast RX Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mcast Rx Cnt | FCS Error Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FCS Error Cnt| Tx Frame Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tx Frame Cnt | Decryption Errors |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Decryption Errs|
+-+-+-+-+-+-+-+-+
Type: 38 for Statistics
Length: 57
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Radio ID: An 8-bit value representing the radio.
Tx Fragment Count: A 32-bit value representing the number of
fragmented frames transmitted.
Multicast Tx Count: A 32-bit value representing the number of
multicast frames transmitted.
Failed Count: A 32-bit value representing the transmit excessive
retries.
Retry Count: A 32-bit value representing the number of transmit
retries.
Multiple Retry Count: A 32-bit value representing the number of
transmits that required more than one retry.
Frame Duplicate Count: A 32-bit value representing the duplicate
frames received.
RTS Success Count: A 32-bit value representing the number of
successfully transmitted Ready To Send (RTS).
RTS Failure Count: A 32-bit value representing the failed
transmitted RTS.
ACK Failure Count: A 32-bit value representing the number of failed
acknowledgements.
Rx Fragment Count: A 32-bit value representing the number of
fragmented frames received.
Multicast RX Count: A 32-bit value representing the number of
multicast frames received.
FCS Error Count: A 32-bit value representing the number of Frame
Check Sequence (FCS) failures.
Decryption Errors: A 32-bit value representing the number of
Decryption errors that occurred on the WTP. Note that this field
is only valid in cases where the WTP provides encryption/
decryption services.
11.8. 802.11 Control Messages
This section will define LWAPP control messages that are specific to
the IEEE 802.11 binding.
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11.8.1. IEEE 802.11 WLAN Config Request
The IEEE 802.11 WLAN Configuration Request is sent by the AC to the
WTP in order to change services provided by the WTP. This control
message is used to either create, update, or delete a WLAN on the
WTP.
The IEEE 802.11 WLAN Configuration Request is sent as a result of
either some manual administrative process (e.g., deleting a WLAN), or
automatically to create a WLAN on a WTP. When sent automatically to
create a WLAN, this control message is sent after the LWAPP
Configuration Request message has been received by the WTP.
Upon receiving this control message, the WTP will modify the
necessary services, and transmit an IEEE 802.11 WLAN Configuration
Response.
An WTP MAY provide service for more than one WLAN: therefore, every
WLAN is identified through a numerical index. For instance, a WTP
that is capable of supporting up to 16 SSIDs could accept up to 16
IEEE 802.11 WLAN Configuration Request messages that include the Add
WLAN message element.
Since the index is the primary identifier for a WLAN, an AC SHOULD
attempt to ensure that the same WLAN is identified through the same
index number on all of its WTPs. An AC that does not follow this
approach MUST find some other means of maintaining a WLAN Identifier
to SSID mapping table.
The following subsections define the message elements that are of
value for this LWAPP operation. Only one message MUST be present.
11.8.1.1. IEEE 802.11 Add WLAN
The Add WLAN message element is used by the AC to define a wireless
LAN on the WTP. The value contains the following format:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | WLAN Capability | WLAN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encryption Policy |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key Index | Shared Key | WPA Data Len |WPA IE Data ...|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RSN Data Len |RSN IE Data ...| Reserved .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WME Data Len |WME IE Data ...| 11e Data Len |11e IE Data ...|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| QoS | Auth Type |Broadcast SSID | Reserved... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSID ... |
+-+-+-+-+-+-+-+-+
Type: 7 for IEEE 802.11 Add WLAN
Length: >= 298
Radio ID: An 8-bit value representing the radio.
WLAN Capability: A 16-bit value containing the capabilities to be
advertised by the WTP within the Probe and Beacon messages.
WLAN ID: A 16-bit value specifying the WLAN Identifier.
Encryption Policy: A 32-bit value specifying the encryption scheme
to apply to traffic to and from the mobile station.
The following values are supported:
0 - Encrypt WEP 104: All packets to/from the mobile station must
be encrypted using a standard 104-bit WEP.
1 - Clear Text: All packets to/from the mobile station do not
require any additional crypto processing by the WTP.
2 - Encrypt WEP 40: All packets to/from the mobile station must
be encrypted using a standard 40-bit WEP.
3 - Encrypt WEP 128: All packets to/from the mobile station must
be encrypted using a standard 128-bit WEP.
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4 - Encrypt AES-CCMP 128: All packets to/from the mobile station
must be encrypted using a 128-bit AES-CCMP [7].
5 - Encrypt TKIP-MIC: All packets to/from the mobile station must
be encrypted using TKIP and authenticated using Michael [16].
6 - Encrypt CKIP: All packets to/from the mobile station must be
encrypted using Cisco TKIP.
Key: A 32-byte session key to use with the encryption policy.
Key-Index: The Key Index associated with the key.
Shared Key: A 1-byte Boolean that specifies whether the key
included in the Key field is a shared WEP key. A value of zero is
used to state that the key is not a shared WEP key, while a value
of one is used to state that the key is a shared WEP key.
WPA Data Len: Length of the WPA Information Element (IE).
WPA IE: A 32-byte field containing the WPA Information Element.
RSN Data Len: Length of the Robust Security Network (RSN) IE.
RSN IE: A 64-byte field containing the RSN Information Element.
Reserved: A 49-byte reserved field, which MUST be set to zero (0).
WME Data Len: Length of the WME IE.
WME IE: A 32-byte field containing the WME Information Element.
DOT11E Data Len: Length of the 802.11e IE.
DOT11E IE: A 32-byte field containing the 802.11e Information
Element.
QOS: An 8-bit value specifying the QoS policy to enforce for the
station.
The following values are supported:
0 - Silver (Best Effort)
1 - Gold (Video)
2 - Platinum (Voice)
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3 - Bronze (Background)
Auth Type: An 8-bit value specifying the station's authentication
type.
The following values are supported:
0 - Open System
1 - WEP Shared Key
2 - WPA/WPA2 802.1X
3 - WPA/WPA2 PSK
Broadcast SSID: A Boolean indicating whether the SSID is to be
broadcast by the WTP. A value of zero disables SSID broadcast,
while a value of one enables it.
Reserved: A 40-byte reserved field.
SSID: The SSID attribute is the service set identifier that will be
advertised by the WTP for this WLAN.
11.8.1.2. IEEE 802.11 Delete WLAN
The Delete WLAN message element is used to inform the WTP that a
previously created WLAN is to be deleted. The value contains the
following fields:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | WLAN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 28 for IEEE 802.11 Delete WLAN
Length: 3
Radio ID: An 8-bit value representing the radio
WLAN ID: A 16-bit value specifying the WLAN Identifier
11.8.1.3. IEEE 802.11 Update WLAN
The Update WLAN message element is used by the AC to define a
wireless LAN on the WTP. The value contains the following format:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | WLAN ID |Encrypt Policy |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encryption Policy | Key... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key Index | Shared Key | WLAN Capability |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 34 for IEEE 802.11 Update WLAN
Length: 43
Radio ID: An 8-bit value representing the radio.
WLAN ID: A 16-bit value specifying the WLAN Identifier.
Encryption Policy: A 32-bit value specifying the encryption scheme
to apply to traffic to and from the mobile station.
The following values are supported:
0 - Encrypt WEP 104: All packets to/from the mobile station must
be encrypted using a standard 104-bit WEP.
1 - Clear Text: All packets to/from the mobile station do not
require any additional crypto processing by the WTP.
2 - Encrypt WEP 40: All packets to/from the mobile station must
be encrypted using a standard 40-bit WEP.
3 - Encrypt WEP 128: All packets to/from the mobile station must
be encrypted using a standard 128-bit WEP.
4 - Encrypt AES-CCMP 128: All packets to/from the mobile station
must be encrypted using a 128-bit AES-CCMP [7].
5 - Encrypt TKIP-MIC: All packets to/from the mobile station must
be encrypted using TKIP and authenticated using Michael [16].
6 - Encrypt CKIP: All packets to/from the mobile station must be
encrypted using Cisco TKIP.
Key: A 32-byte session key to use with the encryption policy.
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Key-Index: The Key Index associated with the key.
Shared Key: A 1-byte Boolean that specifies whether the key
included in the Key field is a shared WEP key. A value of zero
means that the key is not a shared WEP key, while a value of one
is used to state that the key is a shared WEP key.
WLAN Capability: A 16-bit value containing the capabilities to be
advertised by the WTP within the Probe and Beacon messages.
11.8.2. IEEE 802.11 WLAN Config Response
The IEEE 802.11 WLAN Configuration Response is sent by the WTP to the
AC as an acknowledgement of the receipt of an IEEE 802.11 WLAN
Configuration Request.
This LWAPP control message does not include any message elements.
11.8.3. IEEE 802.11 WTP Event
The IEEE 802.11 WTP Event LWAPP message is used by the WTP in order
to report asynchronous events to the AC. There is no reply message
expected from the AC, except that the message is acknowledged via the
reliable transport.
When the AC receives the IEEE 802.11 WTP Event, it will take whatever
action is necessary, depending upon the message elements present in
the message.
The IEEE 802.11 WTP Event message MUST contain one of the following
message elements described in the next subsections.
11.8.3.1. IEEE 802.11 MIC Countermeasures
The MIC Countermeasures message element is sent by the WTP to the AC
to indicate the occurrence of a MIC failure.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | WLAN ID | MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 61 for IEEE 802.11 MIC Countermeasures
Length: 8
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Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP.
WLAN ID: This 8-bit unsigned integer includes the WLAN Identifier,
on which the MIC failure occurred.
MAC Address: The MAC address of the mobile station that caused the
MIC failure.
11.8.3.2. IEEE 802.11 WTP Radio Fail Alarm Indication
The WTP Radio Fail Alarm Indication message element is sent by the
WTP to the AC when it detects a radio failure.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Type | Status | Pad |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 95 for WTP Radio Fail Alarm Indication
Length: 4
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP.
Type: The type of radio failure detected. The following values are
supported:
1 - Receiver
2 - Transmitter
Status: An 8-bit Boolean indicating whether the radio failure is
being reported or cleared. A value of zero is used to clear the
event, while a value of one is used to report the event.
Pad: Reserved field MUST be set to zero (0).
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11.9. Message Element Bindings
The IEEE 802.11 Message Element binding has the following
definitions:
Conf Conf Conf Add
Req Resp Upd Mobile
IEEE 802.11 WTP WLAN Radio Configuration X X X
IEEE 802.11 Rate Set X X
IEEE 802.11 Multi-domain Capability X X X
IEEE 802.11 MAC Operation X X X
IEEE 802.11 Tx Power X X X
IEEE 802.11 Tx Power Level X
IEEE 802.11 Direct Sequence Control X X X
IEEE 802.11 OFDM Control X X X
IEEE 802.11 Supported Rates X X
IEEE 802.11 Antenna X X X
IEEE 802.11 CFP Status X X
IEEE 802.11 Broadcast Probe Mode X X
IEEE 802.11 WTP Mode and Type X? X
IEEE 802.11 WTP Quality of Service X X
IEEE 802.11 MIC Error Report From Mobile X
IEEE 802.11 Update Mobile QoS X
IEEE 802.11 Mobile Session Key X
11.9.1. IEEE 802.11 WTP WLAN Radio Configuration
The WTP WLAN radio configuration is used by the AC to configure a
Radio on the WTP. The message element value contains the following
Fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Reserved | Occupancy Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CFP Per | CFP Maximum Duration | BSS ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BSS ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BSS ID | Beacon Period | DTIM Per |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Country String |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Num Of BSSIDs |
+-+-+-+-+-+-+-+-+
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Type: 8 for IEEE 802.11 WTP WLAN Radio Configuration
Length: 20
Radio ID: An 8-bit value representing the radio to configure.
Reserved: MUST be set to zero
Occupancy Limit: This attribute indicates the maximum amount of
time, in Time Units (TUs), that a point coordinator MAY control
the usage of the wireless medium without relinquishing control for
long enough to allow at least one instance of Distributed
Coordination Function (DCF) access to the medium. The default
value of this attribute SHOULD be 100, and the maximum value
SHOULD be 1000.
CFP Period: The attribute describes the number of DTIM intervals
between the start of Contention-Free Periods (CFPs).
CFP Maximum Duration: The attribute describes the maximum duration
of the CFP in TU that MAY be generated by the Point Coordination
Function (PCF).
BSSID: The WLAN Radio's base MAC address. For WTPs that support
more than a single WLAN, the value of the WLAN Identifier is added
to the last octet of the BSSID. Therefore, a WTP that supports 16
WLANs MUST have 16 MAC addresses reserved for it, and the last
nibble is used to represent the WLAN ID.
Beacon Period: This attribute specifies the number of TUs that a
station uses for scheduling Beacon transmissions. This value is
transmitted in Beacon and Probe Response frames.
DTIM Period: This attribute specifies the number of Beacon
intervals that elapses between transmission of Beacons frames
containing a TIM element whose DTIM Count field is 0. This value
is transmitted in the DTIM Period field of Beacon frames.
Country Code: This attribute identifies the country in which the
station is operating. The first two octets of this string is the
two-character country code as described in document ISO/IEC 3166-
1. The third octet MUST be one of the following:
1. an ASCII space character, if the regulations under which the
station is operating encompass all environments in the country,
2. an ASCII 'O' character, if the regulations under which the station
is operating are for an outdoor environment only, or
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3. an ASCII 'I' character, if the regulations under which the station
is operating are for an indoor environment only.
Number of BSSIDs: This attribute contains the maximum number of
BSSIDs supported by the WTP. This value restricts the number of
logical networks supported by the WTP.
11.9.2. IEEE 802.11 Rate Set
The Rate Set message element value is sent by the AC and contains the
supported operational rates. It contains the following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Rate Set |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 16 for IEEE 802.11 Rate Set
Length: 4
Radio ID: An 8-bit value representing the radio to configure.
Rate Set: The AC generates the Rate Set that the WTP is to include
in its Beacon and Probe messages.
11.9.3. IEEE 802.11 Multi-Domain Capability
The Multi-Domain Capability message element is used by the AC to
inform the WTP of regulatory limits. The value contains the
following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Reserved | First Channel # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Channels | Max Tx Power Level |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 10 for IEEE 802.11 Multi-Domain Capability
Length: 8
Radio ID: An 8-bit value representing the radio to configure.
Reserved: MUST be set to zero
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First Channel #: This attribute indicates the value of the lowest
channel number in the subband for the associated domain country
string.
Number of Channels: This attribute indicates the value of the total
number of channels allowed in the subband for the associated
domain country string.
Max Tx Power Level: This attribute indicates the maximum transmit
power, in dBm, allowed in the subband for the associated domain
country string.
11.9.4. IEEE 802.11 MAC Operation
The MAC Operation message element is sent by the AC to set the 802.11
MAC parameters on the WTP. The value contains the following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Reserved | RTS Threshold |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Short Retry | Long Retry | Fragmentation Threshold |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tx MSDU Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rx MSDU Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 11 for IEEE 802.11 MAC Operation
Length: 16
Radio ID: An 8-bit value representing the radio to configure.
Reserved: MUST be set to zero
RTS Threshold: This attribute indicates the number of octets in a
Management Protocol Data Unit (MPDU), below which an RTS/CTS
(clear to send) handshake MUST NOT be performed. An RTS/CTS
handshake MUST be performed at the beginning of any frame exchange
sequence where the MPDU is of type Data or Management, the MPDU
has an individual address in the Address1 field, and the length of
the MPDU is greater than this threshold. Setting this attribute
to be larger than the maximum MAC Service Data Unit (MSDU) size
MUST have the effect of turning off the RTS/CTS handshake for
frames of Data or Management type transmitted by this Station
(STA). Setting this attribute to zero MUST have the effect of
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turning on the RTS/CTS handshake for all frames of Data or
Management type transmitted by this STA. The default value of
this attribute MUST be 2347.
Short Retry: This attribute indicates the maximum number of
transmission attempts of a frame, the length of which is less than
or equal to RTSThreshold, that MUST be made before a failure
condition is indicated. The default value of this attribute MUST
be 7.
Long Retry: This attribute indicates the maximum number of
transmission attempts of a frame, the length of which is greater
than dot11RTSThreshold, that MUST be made before a failure
condition is indicated. The default value of this attribute MUST
be 4.
Fragmentation Threshold: This attribute specifies the current
maximum size, in octets, of the MPDU that MAY be delivered to the
PHY. An MSDU MUST be broken into fragments if its size exceeds
the value of this attribute after adding MAC headers and trailers.
An MSDU or MAC Management Protocol Data Unit (MMPDU) MUST be
fragmented when the resulting frame has an individual address in
the Address1 field, and the length of the frame is larger than
this threshold. The default value for this attribute MUST be the
lesser of 2346 or the aMPDUMaxLength of the attached PHY and MUST
never exceed the lesser of 2346 or the aMPDUMaxLength of the
attached PHY. The value of this attribute MUST never be less than
256.
Tx MSDU Lifetime: This attribute specifies the elapsed time in TU,
after the initial transmission of an MSDU, after which, further
attempts to transmit the MSDU MUST be terminated. The default
value of this attribute MUST be 512.
Rx MSDU Lifetime: This attribute specifies the elapsed time, in TU,
after the initial reception of a fragmented MMPDU or MSDU, after
which, further attempts to reassemble the MMPDU or MSDU MUST be
terminated. The default value MUST be 512.
11.9.5. IEEE 802.11 Tx Power
The Tx Power message element value is bi-directional. When sent by
the WTP, it contains the current power level of the radio in
question. When sent by the AC, it contains the power level to which
the WTP MUST adhere:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Reserved | Current Tx Power |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 12 for IEEE 802.11 Tx Power
Length: 4
Radio ID: An 8-bit value representing the radio to configure.
Reserved: MUST be set to zero
Current Tx Power: This attribute contains the transmit output power
in mW.
11.9.6. IEEE 802.11 Tx Power Level
The Tx Power Level message element is sent by the WTP and contains
the different power levels supported. The value contains the
following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Num Levels | Power Level [n] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 13 for IEEE 802.11 Tx Power Level
Length: >= 4
Radio ID: An 8-bit value representing the radio to configure.
Num Levels: The number of power level attributes.
Power Level: Each power level fields contains a supported power
level, in mW.
11.9.7. IEEE 802.11 Direct Sequence Control
The Direct Sequence Control message element is a bi-directional
element. When sent by the WTP, it contains the current state. When
sent by the AC, the WTP MUST adhere to the values. This element is
only used for 802.11b radios. The value has the following fields.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Reserved | Current Chan | Current CCA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Energy Detect Threshold |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 14 for IEEE 802.11 Direct Sequence Control
Length: 8
Radio ID: An 8-bit value representing the radio to configure.
Reserved: MUST be set to zero
Current Channel: This attribute contains the current operating
frequency channel of the Direct Sequence Spread Spectrum (DSSS)
PHY.
Current CCA: The current Controlled Channel Access (CCA) method in
operation. Valid values are:
1 - energy detect only (edonly)
2 - carrier sense only (csonly)
4 - carrier sense and energy detect (edandcs)
8 - carrier sense with timer (cswithtimer)
16 - high-rate carrier sense and energy detect (hrcsanded)
Energy Detect Threshold: The current Energy Detect Threshold being
used by the DSSS PHY.
11.9.8. IEEE 802.11 OFDM Control
The Orthogonal Frequency Division Multiplexing (OFDM) Control message
element is a bi-directional element. When sent by the WTP, it
contains the current state. When sent by the AC, the WTP MUST adhere
to the values. This element is only used for 802.11a radios. The
value contains the following fields:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Reserved | Current Chan | Band Support |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TI Threshold |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 15 for IEEE 802.11 OFDM Control
Length: 8
Radio ID: An 8-bit value representing the radio to configure.
Reserved: MUST be set to zero
Current Channel: This attribute contains the current operating
frequency channel of the OFDM PHY.
Band Supported: The capability of the OFDM PHY implementation to
operate in the three U-NII bands. Coded as an integer value of a
3-bit field as follows:
Bit 0 - capable of operating in the lower (5.15-5.25 GHz) U-NII
band
Bit 1 - capable of operating in the middle (5.25-5.35 GHz) U-NII
band
Bit 2 - capable of operating in the upper (5.725-5.825 GHz) U-NII
band
For example, for an implementation capable of operating in the
lower and mid bands, this attribute would take the value.
TI Threshold: The threshold being used to detect a busy medium
(frequency). CCA MUST report a busy medium upon detecting the
RSSI above this threshold.
11.9.9. IEEE 802.11 Antenna
The Antenna message element is communicated by the WTP to the AC to
provide information on the antennas available. The AC MAY use this
element to reconfigure the WTP's antennas. The value contains the
following fields:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Diversity | Combiner | Antenna Cnt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Antenna Selection [0..N] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 41 for IEEE 802.11 Antenna
Length: >= 8
Radio ID: An 8-bit value representing the radio to configure.
Diversity: An 8-bit value specifying whether the antenna is to
provide receive diversity. The following values are supported:
0 - Disabled
1 - Enabled (may only be true if the antenna can be used as a
receive antenna)
Combiner: An 8-bit value specifying the combiner selection. The
following values are supported:
1 - Sectorized (Left)
2 - Sectorized (Right)
3 - Omni
4 - Mimo
Antenna Count: An 8-bit value specifying the number of Antenna
Selection fields.
Antenna Selection: One 8-bit antenna configuration value per
antenna in the WTP. The following values are supported:
1 - Internal Antenna
2 - External Antenna
11.9.10. IEEE 802.11 Supported Rates
The Supported Rates message element is sent by the WTP to indicate
the rates that it supports. The value contains the following fields:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Supported Rates |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 16 for IEEE 802.11 Supported Rates
Length: 4
Radio ID: An 8-bit value representing the radio.
Supported Rates: The WTP includes the Supported Rates that its
hardware supports. The format is identical to the Rate Set
message element.
11.9.11. IEEE 802.11 CFP Status
The CFP Status message element is sent to provide the CF Polling
configuration.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 48 for IEEE 802.11 CFP Status
Length: 2
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP.
Status: An 8-bit Boolean containing the status of the CF Polling
feature. A value of zero disables CFP Status, while a value of
one enables it.
11.9.12. IEEE 802.11 WTP Mode and Type
The WTP Mode and Type message element is used to configure a WTP to
operate in a specific mode.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mode | Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 54 for IEEE 802.11 WTP Mode and Type
Length: 2
Mode: An 8-bit value describing the type of information being sent.
The following values are supported:
0 - Split MAC
2 - Local MAC
Type: The type field is not currently used.
11.9.13. IEEE 802.11 Broadcast Probe Mode
The Broadcast Probe Mode message element indicates whether a WTP will
respond to NULL SSID Probe requests. Since broadcast NULL Probes are
not sent to a specific BSSID, the WTP cannot know which SSID the
sending station is querying. Therefore, this behavior must be global
to the WTP.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Status |
+-+-+-+-+-+-+-+-+
Type: 51 for IEEE 802.11 Broadcast Probe Mode
Length: 1
Status: An 8-bit Boolean indicating the status of whether a WTP
shall respond to a NULL SSID Probe request. A value of zero
disables the NULL SSID Probe response, while a value of one
enables it.
11.9.14. IEEE 802.11 WTP Quality of Service
The WTP Quality of Service message element value is sent by the AC to
the WTP to communicate quality-of-service configuration information.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Tag Packets |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 57 for IEEE 802.11 WTP Quality of Service
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Length: 12
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP.
Tag Packets: A value indicating whether LWAPP packets should be
tagged for QoS purposes. The following values are currently
supported:
0 - Untagged
1 - 802.1P
2 - DSCP
Immediately following the above header is the following data
structure. This data structure will be repeated five times, once
for every QoS profile. The order of the QoS profiles is Uranium,
Platinum, Gold, Silver, and Bronze.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Queue Depth | CWMin | CWMax |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CWMax | AIFS | CBR |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Dot1P Tag | DSCP Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Queue Depth: The number of packets that can be on the specific QoS
transmit queue at any given time.
CWMin: The Contention Window minimum value for the QoS transmit
queue.
CWMax: The Contention Window maximum value for the QoS transmit
queue.
AIFS: The Arbitration Inter Frame Spacing to use for the QoS
transmit queue.
CBR: The Constant Bit Rate (CBR) value to observe for the QoS
transmit queue.
Dot1P Tag: The 802.1P precedence value to use if packets are to be
802.1P tagged.
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DSCP Tag: The DSCP label to use if packets are to be DSCP tagged.
11.9.15. IEEE 802.11 MIC Error Report From Mobile
The MIC Error Report From Mobile message element is sent by an AC to
a WTP when it receives a MIC failure notification via the Error bit
in the EAP over LAN (EAPOL)-Key frame.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Client MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Client MAC Address | BSSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BSSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | WLAN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 79 for IEEE 802.11 MIC Error Report From Mobile
Length: 14
Client MAC Address: The Client MAC address of the station reporting
the MIC failure.
BSSID: The BSSID on which the MIC failure is being reported.
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP.
WLAN ID: The WLAN ID on which the MIC failure is being reported.
11.10. IEEE 802.11 Message Element Values
This section lists IEEE 802.11-specific values for any generic LWAPP
message elements that include fields whose values are technology-
specific.
IEEE 802.11 uses the following values:
4 - Encrypt AES-CCMP 128: WTP supports AES-CCMP, as defined in [7].
5 - Encrypt TKIP-MIC: WTP supports TKIP and Michael, as defined in
[16].
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12. LWAPP Protocol Timers
A WTP or AC that implements LWAPP discovery MUST implement the
following timers.
12.1. MaxDiscoveryInterval
The maximum time allowed between sending Discovery Requests from the
interface, in seconds. Must be no less than 2 seconds and no greater
than 180 seconds.
Default: 20 seconds.
12.2. SilentInterval
The minimum time, in seconds, a WTP MUST wait after failing to
receive any responses to its Discovery Requests, before it MAY again
send Discovery Requests.
Default: 30
12.3. NeighborDeadInterval
The minimum time, in seconds, a WTP MUST wait without having received
Echo Responses to its Echo Requests, before the destination for the
Echo Request may be considered dead. Must be no less than
2*EchoInterval seconds and no greater than 240 seconds.
Default: 60
12.4. EchoInterval
The minimum time, in seconds, between sending Echo Requests to the AC
with which the WTP has joined.
Default: 30
12.5. DiscoveryInterval
The minimum time, in seconds, that a WTP MUST wait after receiving a
Discovery Response, before sending a Join Request.
Default: 5
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12.6. RetransmitInterval
The minimum time, in seconds, that a non-acknowledged LWAPP packet
will be retransmitted.
Default: 3
12.7. ResponseTimeout
The minimum time, in seconds, in which an LWAPP Request message must
be responded to.
Default: 1
12.8. KeyLifetime
The maximum time, in seconds, that an LWAPP session key is valid.
Default: 28800
13. LWAPP Protocol Variables
A WTP or AC that implements LWAPP discovery MUST allow for the
following variables to be configured by system management; default
values are specified so as to make it unnecessary to configure any of
these variables in many cases.
13.1. MaxDiscoveries
The maximum number of Discovery Requests that will be sent after a
WTP boots.
Default: 10
13.2. DiscoveryCount
The number of discoveries transmitted by a WTP to a single AC. This
is a monotonically increasing counter.
13.3. RetransmitCount
The number of retransmissions for a given LWAPP packet. This is a
monotonically increasing counter.
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13.4. MaxRetransmit
The maximum number of retransmissions for a given LWAPP packet before
the link layer considers the peer dead.
Default: 5
14. NAT Considerations
There are two specific situations where a NAT system may be used in
conjunction with LWAPP. The first consists of a configuration where
the WTP is behind a NAT system. Given that all communication is
initiated by the WTP, and all communication is performed over IP
using a single UDP port, the protocol easily traverses NAT systems in
this configuration.
The second configuration is one where the AC sits behind a NAT, and
there are two main issues that exist in this situation. First, an AC
communicates its interfaces and associated WTP load on these
interfaces, through the WTP Manager Control IP Address. This message
element is currently mandatory, and if NAT compliance became an
issue, it would be possible to either:
1. make the WTP Manager Control IP Address optional, allowing the WTP
to simply use the known IP address. However, note that this
approach would eliminate the ability to perform load balancing of
WTP across ACs, and therefore is not the recommended approach.
2. allow an AC to be able to configure a NAT'ed address for every
associated AC that would generally be communicated in the WTP
Manager Control IP Address message element.
3. require that if a WTP determines that the AC List message element
consists of a set of IP addresses that are different from the AC's
IP address it is currently communicating with, then assume that
NAT is being enforced, and require that the WTP communicate with
the original AC's IP address (and ignore the WTP Manager Control
IP Address message element(s)).
Another issue related to having an AC behind a NAT system is LWAPP's
support for the CAPWAP Objective to allow the control and data plane
to be separated. In order to support this requirement, the LWAPP
protocol defines the WTP Manager Data IP Address message element,
which allows the AC to inform the WTP that the LWAPP data frames are
to be forwarded to a separate IP address. This feature MUST be
disabled when an AC is behind a NAT. However, there is no easy way
to provide some default mechanism that satisfies both the data/
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control separation and NAT objectives, as they directly conflict with
each other. As a consequence, user intervention will be required to
support such networks.
LWAPP has a feature that allows for all of the AC's identities
supporting a group of WTPs to be communicated through the AC List
message element. This feature must be disabled when the AC is behind
a NAT and the IP address that is embedded would be invalid.
The LWAPP protocol has a feature that allows an AC to configure a
static IP address on a WTP. The WTP Static IP Address Information
message element provides such a function; however, this feature
SHOULD NOT be used in NAT'ed environments, unless the administrator
is familiar with the internal IP addressing scheme within the WTP's
private network, and does not rely on the public address seen by the
AC.
When a WTP detects the duplicate address condition, it generates a
message to the AC, which includes the Duplicate IP Address message
element. Once again, it is important to note that the IP address
embedded within this message element would be different from the
public IP address seen by the AC.
15. Security Considerations
LWAPP uses either an authenticated key exchange or key agreement
mechanism to ensure peer authenticity and establish fresh session
keys to protect the LWAPP communications.
The LWAPP protocol defines a join phase, which allows a WTP to bind a
session with an AC. During this process, a session key is mutually
derived, and secured either through an X.509 certificate or a pre-
shared key. The resulting key exchange generates an encryption
session key, which is used to encrypt the LWAPP control packets, and
a key derivation key.
During the established secure communication, the WTP and AC may rekey
using the key update process, which is identical to the join phase,
meaning the session keys are mutually derived. However, the exchange
described for pre-shared session keys is always used for the key
update, with the pre-shared key set to the derivation key created
either during the join, or the last key update if one has occurred.
The key update results in a new derivation key, which is used in the
next key update, as well as an encryption session key to encrypt the
LWAPP control packets.
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Replay protection of the Join Request is handled through an exchange
of nonces during the join (or key update) phase. The Join Request
includes an XNonce, which is included in the AC's authenticated Join
Reply's encrypted ANonce message element, allowing for the two
messages to be bound. Upon receipt of the Join Reply, the WTP
generates the WNonce, and generates a set of session keys using a KDF
function. One of these keys is used to MIC the Join ACK. The AC
responds with a Join Confirm, which must also include a MIC, and
therefore be capable of deriving the same set of session keys.
In both the X.509 certificate and pre-shared key modes, an
initialization vector is created through the above mentioned KDF
function. The IV and the KDF created encryption key are used to
encrypt the LWAPP control frames.
Given that authentication in the Join exchange does not occur until
the WTP transmits the Join ACK message, it is crucial that an AC not
delete any state for a WTP it is servicing until an authentication
Join ACK has been received. Otherwise, a potential Denial-of-Service
attack exists, whereby sending a spoofed Join Request for a valid WTP
would cause the AC to reset the WTP's connection.
It is important to note that Perfect Forward Secrecy is not a
requirement for the LWAPP protocol.
Note that the LWAPP protocol does not add any new vulnerabilities to
802.11 infrastructure that makes use of WEP for encryption purposes.
However, implementors SHOULD discourage the use of WEP to allow the
market to move towards technically sound cryptographic solutions,
such as 802.11i.
15.1. Certificate-Based Session Key Establishment
LWAPP uses public key cryptography to ensure trust between the WTP
and the AC. One question that periodically arises is why the Join
Request is not signed. Signing this request would not be optimal for
the following reasons:
1. The Join Request is replayable, so a signature doesn't provide
much protection unless the switches keep track of all previous
Join Requests from a given WTP.
2. Replay detection is handled during the Join Reply and Join ACK
messages.
3. A signed Join Request provides a potential Denial-of-Service
attack on the AC, which would have to authenticate each
(potentially malicious) message.
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The WTP-Certificate that is included in the Join Request MUST be
validated by the AC. It is also good practice that the AC perform
some form of authorization, ensuring that the WTP in question is
allowed to establish an LWAPP session with it.
15.2. PSK-Based Session Key Establishment
Use of a fixed shared secret of limited entropy (for example, a PSK
that is relatively short, or was chosen by a human and thus may
contain less entropy than its length would imply) may allow an
attacker to perform a brute-force or dictionary attack to recover the
secret.
It is RECOMMENDED that implementations that allow the administrator
to manually configure the PSK also provide a functionality for
generating a new random PSK, taking RFC 1750 [4] into account.
Since the key generation does not expose the nonces in plaintext,
there are no practical passive attacks possible.
16. Acknowledgements
The authors wish to thank Michael Vakulenko for contributing text
that describes how LWAPP can be used over a Layer 3 (IP) network.
The authors would also like to thanks Russ Housley and Charles Clancy
for their assistance in providing a security review of the LWAPP
specification. Charles' review can be found in [12].
17. References
17.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] National Institute of Standards and Technology, "Advanced
Encryption Standard (AES)", FIPS PUB 197, November 2001,
<http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf>.
[3] Whiting, D., Housley, R., and N. Ferguson, "Counter with CBC-
MAC (CCM)", RFC 3610, September 2003.
[4] Eastlake, D., 3rd, Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 2005.
[5] Manner, J., Ed., and M. Kojo, Ed., "Mobility Related
Terminology", RFC 3753, June 2004.
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[6] "Information technology - Telecommunications and information
exchange between systems - Local and metropolitan area networks
- Specific requirements - Part 11: Wireless LAN Medium Access
Control (MAC) and Physical Layer (PHY) specifications", IEEE
Standard 802.11, 2007,
<http://standards.ieee.org/getieee802/download/802.11-2007.pdf>
[7] "Information technology - Telecommunications and information
exchange between systems - Local and metropolitan area networks
- Specific requirements - Part 11: Wireless LAN Medium Access
Control (MAC) and Physical Layer (PHY) specifications Amendment
6: Medium Access Control (MAC) Security Enhancements", IEEE
Standard 802.11i, July 2004,
http://standards.ieee.org/getieee802/download/802.11i-2004.pdf
[8] Clark, D., "IP datagram reassembly algorithms", RFC 815, July
1982.
[9] Schaad, J. and R. Housley, "Advanced Encryption Standard (AES)
Key Wrap Algorithm", RFC 3394, September 2002.
[10] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley,
R., and W. Polk, "Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile", RFC
5280, May 2008.
[11] "Netscape-Defined Certificate Extensions",
<http://www.redhat.com/docs/manuals/cert-
system/admin/7.1/app_ext.html#35336>.
[12] Clancy, C., "Security Review of the Light-Weight Access Point
Protocol", May 2005,
<http://www.cs.umd.edu/~clancy/docs/lwapp-review.pdf>.
17.2. Informative References
[13] Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced by
an On-line Database", RFC 3232, January 2002.
[14] Kent, S. and K. Seo, "Security Architecture for the Internet
Protocol", RFC 4301, December 2005.
[15] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997.
[16] "WiFi Protected Access (WPA) rev 1.6", April 2003.
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Authors' Addresses
Pat R. Calhoun
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
Phone: +1 408-853-5269
EMail: pcalhoun@cisco.com
Rohit Suri
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
Phone: +1 408-853-5548
EMail: rsuri@cisco.com
Nancy Cam-Winget
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
Phone: +1 408-853-0532
EMail: ncamwing@cisco.com
Scott Kelly
EMail: scott@hyperthought.com
Michael Glenn Williams
GWhiz Arts & Sciences
1560 Newbury Road, Suite 1-204
Newbury Park, CA 91320
Phone: +1 805-499-1994
EMail: gwhiz@gwhiz.com
Sue Hares
Phone: +1 734-604-0332
EMail: shares@ndzh.com
Bob O'Hara
EMail: bob.ohara@computer.org
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