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Internet Engineering Task Force (IETF) K. Kinnear
Request for Comments: 6926 M. Stapp
Category: Standards Track Cisco Systems, Inc.
ISSN: 2070-1721 R. Desetti
B. Joshi
Infosys Ltd.
N. Russell
Sea Street Technologies Inc.
P. Kurapati
Juniper Networks
B. Volz
Cisco Systems, Inc.
April 2013
DHCPv4 Bulk Leasequery
Abstract
The Dynamic Host Configuration Protocol for IPv4 (DHCPv4) Leasequery
protocol allows a requestor to request information about DHCPv4
bindings. This protocol is limited to queries for individual
bindings. In some situations, individual binding queries may not be
efficient or even possible. This document extends the DHCPv4
Leasequery protocol to allow for bulk transfer of DHCPv4 address
binding data via TCP.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
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/rfc6926.
Kinnear, et al. Standards Track [Page 1]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
Copyright Notice
Copyright (c) 2013 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. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Kinnear, et al. Standards Track [Page 2]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
Table of Contents
1. Introduction ....................................................4
2. Terminology .....................................................5
3. Design Goals ....................................................8
3.1. Information Acquisition before Data Starts .................8
3.2. Lessen Need for Caching and Negative Caching ...............8
3.3. Antispoofing in 'Fast Path' ................................8
3.4. Minimize Data Transmission .................................9
4. Protocol Overview ...............................................9
5. Interaction between UDP Leasequery and Bulk Leasequery .........11
6. Message and Option Definitions .................................12
6.1. Message Framing for TCP ...................................12
6.2. New or Changed Options ....................................13
6.3. Connection and Transmission Parameters ....................20
7. Requestor Behavior .............................................21
7.1. Connecting and General Processing .........................21
7.2. Forming a Bulk Leasequery .................................21
7.3. Processing Bulk Replies ...................................23
7.4. Processing Time Values in Leasequery Messages .............25
7.5. Querying Multiple Servers .................................26
7.6. Making Sense out of Multiple Responses concerning
a Single IPv4 Address .....................................26
7.7. Multiple Queries to a Single Server over One Connection ...27
7.8. Closing Connections .......................................28
8. Server Behavior ................................................29
8.1. Accepting Connections .....................................29
8.2. Replying to a Bulk Leasequery .............................29
8.3. Building a Single Reply for Bulk Leasequery ...............33
8.4. Multiple or Parallel Queries ..............................34
8.5. Closing Connections .......................................35
9. Security Considerations ........................................35
10. IANA Considerations ...........................................37
11. Acknowledgements ..............................................38
12. References ....................................................38
12.1. Normative References .....................................38
12.2. Informative References ...................................39
Kinnear, et al. Standards Track [Page 3]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
1. Introduction
DHCPv4 [RFC2131] [RFC2132] specifies a protocol for the assignment of
IPv4 address and configuration information to IPv4 nodes. DHCPv4
servers maintain authoritative binding information.
+--------+
| DHCPv4 | +--------------+
| Server |-...-| DHCP |
| | | Relay Agent |
+--------+ +--------------+
| |
+------+ +------+
|Modem1| |Modem2|
+------+ +------+
| | |
+-----+ +-----+ +-----+
|Node1| |Node2| |Node3|
+-----+ +-----+ +-----+
Figure 1: Example DHCPv4 Configuration
DHCPv4 relay agents receive DHCPv4 messages and frequently append a
Relay Agent Information option [RFC3046] before relaying them to the
configured DHCPv4 servers (see Figure 1). In this process, some
relay agents also glean lease information sent by the server and
cache it locally. This information is used for a variety of
purposes. Two examples are prevention of spoofing attempts from the
DHCPv4 clients and installation of routes. When a relay agent
reboots, this information is frequently lost.
The DHCPv4 Leasequery capability [RFC4388] extends the basic DHCPv4
capability to allow an external entity, such as a relay agent, to
query a DHCPv4 server to rapidly recover lease state information
about a particular IP address or client.
The existing query types in Leasequery are typically data driven; the
relay agent initiates the Leasequery when it receives data traffic
from or to the client. This approach may not scale well when there
are thousands of clients connected to the relay agent or when the
relay agent has a need to rebuild its internal data store prior to
processing traffic in one direction or another.
Some applications require the ability to query the server without
waiting for traffic from or to clients. This query capability, in
turn, requires an underlying transport more suitable to the bulk
transmission of data.
Kinnear, et al. Standards Track [Page 4]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
This document extends the DHCPv4 Leasequery protocol [RFC4388] to add
support for queries that address these additional requirements.
There may be many thousands of DHCPv4 bindings returned as the result
of a single request, so TCP [RFC4614] is specified for efficiency of
data transfer. We define several additional query types, each of
which can return multiple responses, in order to meet a variety of
requirements.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119].
This document uses the following terms:
o "absolute time"
Absolute time is a 32-bit quantity containing the number of
seconds since January 1, 1970.
o "access concentrator"
An access concentrator is a router or switch at the broadband
access provider's edge of a public broadband access network. This
document assumes that the access concentrator includes the DHCPv4
relay agent functionality, for example, a CMTS (Cable Modem
Termination System) in a cable environment or a DSLAM (Digital
Subscriber Line Access Multiplexer) in a DSL environment.
o "active binding"
An IP address with an active binding refers to an IP address that
is currently associated with a DHCPv4 client where that DHCPv4
client has the right to use the IP address.
o "Bulk Leasequery"
Bulk Leasequery involves requesting and receiving the existing
DHCPv4 address binding information in an efficient manner.
o "clock skew"
The clock skew for a Bulk Leasequery connection is the difference
between the absolute time on a DHCPv4 server and the absolute time
on the system where a requestor of a Bulk Leasequery is executing.
It is not absolutely constant but is likely to vary only slowly.
Kinnear, et al. Standards Track [Page 5]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
It is possible that, when both systems run NTP, the clock skew is
negligible; this is not only acceptable but desired.
While it is easy to think that this can be calculated precisely
after one message is received by a requestor from a DHCPv4 server,
a more accurate value is derived from continuously examining the
instantaneous value developed from each message received from a
DHCPv4 server and using it to make small adjustments to the
existing value held in the requestor.
o "Default VPN"
A default VPN indicates that the address being described belongs
to the set of addresses not part of any VPN (in other words, the
normal address space operated on by DHCP). This includes Special
Use IPv4 Addresses as defined in [RFC5735].
o "DHCPv4 client"
A DHCPv4 client is an Internet node using DHCPv4 to obtain
configuration parameters such as a network address.
o "DHCPv4 relay agent"
A DHCPv4 relay agent is an agent that is neither a DHCPv4 client
nor a DHCP server that transfers BOOTP and DHCPv4 messages between
clients and servers residing on different subnets, per [RFC951]
and [RFC1542].
o "DHCPv4 server"
A DHCPv4 server is an Internet node that returns configuration
parameters to DHCPv4 clients.
o "DSLAM"
DSLAM stands for Digital Subscriber Line Access Multiplexer.
o "downstream"
Downstream refers to a direction away from the central part of a
network and toward the edge. In a DHCPv4 context, this typically
refers to a network direction that is away from the DHCPv4 server
and toward the DHCPv4 client.
o "Global VPN"
Global VPN is another name for the default VPN.
Kinnear, et al. Standards Track [Page 6]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
o "IP address"
In this document, the term "IP address" refers to an IPv4 IP
address.
o "IP address binding"
An IP address binding is the information that a DHCPv4 server
keeps regarding the relationship between a DHCPv4 client and an IP
address. This includes the identity of the DHCPv4 client and the
expiration time, if any, of any lease that client has on a
particular IP address. In some contexts, this may include
information on IP addresses that are currently associated with
DHCPv4 clients, and in others, it may also include IP addresses
with no current association to a DHCPv4 client.
o "MAC address"
In the context of a DHCPv4 message, a Media Access Control (MAC)
address consists of the fields: hardware type "htype", hardware
length "hlen", and client hardware address "chaddr".
o "upstream"
Upstream refers to a direction toward the central part of a
network and away from the edge. In a DHCPv4 context, this
typically refers to a network direction that is away from the
DHCPv4 client and toward the DHCPv4 server.
o "stable storage"
Stable storage is used to hold information concerning IP address
bindings (among other things) so that this information is not lost
in the event of a failure that requires restart of the network
element. DHCPv4 servers are typically expected to have high-speed
access to stable storage, while relay agents and access
concentrators usually do not have access to stable storage,
although they may have periodic access to such storage.
o "xid"
Transaction-id. The term "xid" refers to the DHCPv4 field
containing the transaction-id of the message.
Kinnear, et al. Standards Track [Page 7]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
3. Design Goals
The goal of this document is to provide a lightweight protocol for an
access concentrator or other network element (such as a DHCP relay
agent) to retrieve IP address binding information available in the
DHCPv4 server. The protocol should also allow an access concentrator
or DHCP relay agent to retrieve consolidated IP address binding
information for either the entire access concentrator or a single
connection/circuit. Throughout the discussion below, everything that
applies to an access concentrator also applies to a DHCP relay agent.
3.1. Information Acquisition before Data Starts
The existing data-driven approach required by [RFC4388] means that
the Leasequeries can only be performed after an access concentrator
receives data. To implement antispoofing, the concentrator must drop
messages for each client until it gets lease information from the
DHCPv4 server for that client. If an access concentrator finishes
the Leasequeries before it starts receiving data, then there is no
need to drop legitimate messages. In this way, outage time may be
reduced.
3.2. Lessen Need for Caching and Negative Caching
The result of a single Leasequery should be cached, whether that
results in a positive or negative cache, in order to remember that
the Leasequery was performed. This caching is required to limit the
traffic imposed upon a DHCPv4 server by Leasequeries for information
already received.
These caches not only consume precious resources, they also need to
be managed. Hence, they should be avoided as much as possible. One
of the goals of the DHCPv4 Bulk Leasequery is to reduce the need for
this sort of caching.
3.3. Antispoofing in 'Fast Path'
If antispoofing is not done in the fast path, it will become a
bottleneck and may lead to denial of service of the access
concentrator. The Leasequeries should make it possible to do
antispoofing in the fast path.
Kinnear, et al. Standards Track [Page 8]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
3.4. Minimize Data Transmission
It may be that a network element is able to periodically save its
entire list of assigned IP addresses to some form of stable storage.
In this case, it will wish to recover all of the updates to this
information without duplicating the information it has recovered from
its own stable storage.
Bulk Leasequery allows the specification of a query-start-time as
well as a query-end-time. Use of query times allows a network
element that periodically commits information to stable storage to
recover just what it lost since the last commit.
4. Protocol Overview
The DHCPv4 Bulk Leasequery protocol is modeled on the existing
individual DHCPv4 Leasequery protocol in [RFC4388] as well as related
work on DHCPv6 Bulk Leasequery [RFC5460]. A Bulk Leasequery
requestor opens a TCP connection to a DHCPv4 server using the DHCPv4
port 67. Note that this implies that the Leasequery requestor has
server IP address(es) available via configuration or some other means
and that it has unicast IP reachability to the DHCPv4 server. No
relaying of Bulk Leasequery messages is specified.
After establishing a connection, the requestor sends a
DHCPBULKLEASEQUERY message over the connection.
The server uses the message type and additional data in the DHCPv4
DHCPBULKLEASEQUERY message to identify any relevant bindings.
In order to support some query types, servers may have to maintain
additional data structures or otherwise be able to locate bindings
that have been requested by the Leasequery requestor.
Relevant bindings are returned in DHCPv4 messages with either the
DHCPLEASEACTIVE message type for an IP address with a currently
active lease or, in some situations, a DHCPLEASEUNASSIGNED message
type for an IP address that is controlled by the DHCPv4 server but is
not actively leased by a DHCPv4 client at the present time.
The Bulk Leasequery protocol is designed to provide an external
entity with information concerning existing DHCPv4 IPv4 address
bindings managed by the DHCPv4 server. When complete, the DHCPv4
server will send a DHCPLEASEQUERYDONE message. If a connection is
lost while processing a Bulk Leasequery, the Bulk Leasequery must be
retried as there is no provision for determining the extent of data
already received by the requestor for a Bulk Leasequery.
Kinnear, et al. Standards Track [Page 9]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
Bulk Leasequery supports queries by MAC address and by Client
Identifier in a way similar to [RFC4388]. The Bulk Leasequery
protocol also adds several new queries.
o Query by Relay Identifier
This query asks a server for the bindings associated with a
specific relay agent; the relay agent is identified by a Relay
Agent Identifier carried in a Relay-ID sub-option [RFC6925].
Relay agents can include this sub-option while relaying messages
to DHCPv4 servers. Servers can retain the Relay-ID and associate
it with bindings made on behalf of the relay agent's clients. The
bindings returned are only those for DHCPv4 clients with a
currently active binding.
o Query by Remote ID
This query asks a server for the bindings associated with a relay
agent Remote ID sub-option [RFC3046] value. The bindings returned
are only those for DHCPv4 clients with a currently active binding.
o Query for All Configured IP Addresses
This query asks a server for information concerning all IP
addresses configured in that DHCPv4 server by specifying no other
type of query. In this case, the bindings returned are for all
configured IP addresses, whether or not they contain a currently
active binding to a DHCPv4 client, since one point of this type of
query is to update an existing database with changes after a
particular point in time.
Any of the above queries can be qualified by the specification of a
query-start-time or a query-end-time (or both). When these timers
are used as qualifiers, they indicate that a binding should be
included if it changed on or after the query-start-time and on or
before the query-end-time.
In addition, any of the above queries can be qualified by the
specification of a VPN-ID option [RFC6607] to select the VPN on which
the query should be processed. The VPN-ID option is also extended to
allow queries across all available VPNs. In the absence of any VPN-
ID option, only the default (global) VPN is used to satisfy the
query.
Kinnear, et al. Standards Track [Page 10]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
5. Interaction between UDP Leasequery and Bulk Leasequery
Bulk Leasequery can be seen as an extension of the existing UDP
Leasequery protocol [RFC4388]. This section clarifies the
relationship between the two protocols.
The Bulk Leasequery TCP connection is only designed to handle the
DHCPBULKLEASEQUERY request. It is not intended as an alternative
DHCPv4 communication option for clients seeking other DHCPv4
services. DHCPv4 address allocation could not be performed over a
TCP connection in any case, as a TCP connection requires an IP
address and no IPv4 address exists prior to a successful DHCPv4
address allocation exchange. In addition, the existing DHCPv4 UDP
transmission regime is implemented in untold millions of devices
deployed worldwide, and complicating DHCPv4 services with alternative
transmission approaches (even if it were possible) would be worse
than any perceived benefit to doing so.
Two of the query types introduced in the UDP Leasequery protocol can
be used in the Bulk Leasequery protocol -- Query by MAC address and
Query by Client-identifier.
The contents of the reply messages are similar between the existing
UDP Leasequery protocol and the Bulk Leasequery protocol, though more
information is returned in the Bulk Leasequery messages.
One change in behavior for these existing queries is required when
Bulk Leasequery is used. Sections 6.1, 6.4.1, and 6.4.2 of [RFC4388]
specify the use of an associated-ip option in DHCPLEASEACTIVE
messages in cases where multiple bindings were found. When Bulk
Leasequery is used, this mechanism is not necessary; a server
returning multiple bindings simply does so directly as specified in
this document. The associated-ip option MUST NOT appear in Bulk
Leasequery replies.
Implementors should note that the TCP message framing defined in
Section 6.1 is not compatible with the UDP message format. If a TCP-
framed request is sent as a UDP message, it may not be valid, because
protocol fields will be offset by the message-size prefix.
Kinnear, et al. Standards Track [Page 11]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
6. Message and Option Definitions
6.1. Message Framing for TCP
The use of TCP for the Bulk Leasequery protocol permits multiple
messages to be sent from one end of the connection to the other
without requiring a request/response paradigm as does UDP DHCPv4
[RFC2131]. The receiver needs to be able to determine the size of
each message it receives. Two octets containing the message size in
network byte order are prepended to each DHCPv4 message sent on a
Bulk Leasequery TCP connection. The two message-size octets 'frame'
each DHCPv4 message.
The maximum message size is 65535 octets.
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-size | op (1) | htype (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| hlen (1) | hops (1) | .... |
+---------------+---------------+ +
| |
. remainder of DHCPv4 message,
. from Figure 1 of [RFC2131] .
. .
. (variable) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
message-size the number of octets in the message that
follows, as a 16-bit unsigned integer in
network byte order.
All other fields are as specified in DHCPv4 [RFC2131].
Figure 2: Format of a DHCPv4 Message in TCP
The intent in using this format is that code that currently knows how
to deal with sending or receiving a message in [RFC2131] format will
easily be able to deal with the message contained in the TCP framing.
Kinnear, et al. Standards Track [Page 12]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
6.2. New or Changed Options
The existing messages DHCPLEASEUNASSIGNED and DHCPLEASEACTIVE are
used as the value of the dhcp-message-type option to indicate an IP
address that is currently not leased or currently leased to a DHCPv4
client, respectively [RFC4388].
Additional options have also been defined to enable the Bulk
Leasequery protocol to communicate useful information to the
requestor.
6.2.1. dhcp-message-type
The dhcp-message-type option (option 53) from Section 9.6 of
[RFC2132] requires new values. The values of these message types are
shown below in an extension of the table from Section 9.6 of
[RFC2132]:
Value Message Type
----- ------------
14 DHCPBULKLEASEQUERY
15 DHCPLEASEQUERYDONE
6.2.2. status-code
The status-code option allows a machine-readable value to be returned
regarding the status of a DHCPBULKLEASEQUERY request.
This option has two possible scopes when used with Bulk Leasequery,
depending on the context in which it appears. It refers to the
information in a single Leasequery reply if the value of the dhcp-
message-type is DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED. It refers to
the message stream related to an entire request if the value of the
dhcp-message-type is DHCPLEASEQUERYDONE.
The code for this option is 151. The length of this option is a
minimum of 1 octet.
Status Status
Code Len Code Message
+------+------+------+------+------+-- --+-----+
| 151 | n+1 |status| s1 | s2 | ... | sn |
+------+------+------+------+------+-- --+-----+
Kinnear, et al. Standards Track [Page 13]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
The status-code is indicated in one octet as defined in the table
below. The Status Message is an optional UTF-8-encoded text string
suitable for display to an end user. This text string MUST NOT
contain a termination character (e.g., a null). The Len field
describes the length of the Status Message without any terminator
character. Null characters MUST NOT appear in the Status Message
string, and it is a protocol violation for them to appear in any
position in the Status Message, including at the end.
Name Status Code Description
---- ----------- -----------
Success 000 Success. Also signaled by absence of
a status-code option.
UnspecFail 001 Failure, reason unspecified.
QueryTerminated 002 Indicates that the server is unable to
perform a query or has prematurely terminated
the query for some reason (which should be
communicated in the text message).
MalformedQuery 003 The query was not understood.
NotAllowed 004 The query or request was understood but was
not allowed in this context.
A status-code option MAY appear in the options field of a DHCPv4
message. If the status-code option does not appear, it is assumed
that the operation was successful. The status-code option SHOULD NOT
appear in a message that is successful unless there is some text
string that needs to be communicated to the requestor.
6.2.3. base-time
The base-time option is the current time the message was created to
be sent by the DHCPv4 server to the requestor of the Bulk Leasequery.
This MUST be an absolute time. All of the other time-based options
in the reply message are relative to this time, including the dhcp-
lease-time [RFC2132] and client-last-transaction-time [RFC4388].
This time is in the context of the DHCPv4 server that placed this
option in a message.
This is an unsigned integer in network byte order.
Kinnear, et al. Standards Track [Page 14]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
The code for this option is 152. The length of this option is 4
octets.
DHCPv4 Server
Code Len base-time
+-----+-----+-----+-----+-----+-----+
| 152 | 4 | t1 | t2 | t3 | t4 |
+-----+-----+-----+-----+-----+-----+
6.2.4. start-time-of-state
The start-time-of-state option allows the receiver to determine the
time at which the IP address made the transition into its current
state.
This MUST NOT be an absolute time, which is equivalent to saying that
this MUST NOT be an absolute number of seconds since January 1, 1970.
Instead, this MUST be the unsigned integer number of seconds from the
time the IP address transitioned its current state to the time
specified in the base-time option in the same message.
This is an unsigned integer in network byte order.
The code for this option is 153. The length of this option is 4
octets.
Seconds in the past
Code Len from base-time
+-----+-----+-----+-----+-----+-----+
| 153 | 4 | t1 | t2 | t3 | t4 |
+-----+-----+-----+-----+-----+-----+
6.2.5. query-start-time
The query-start-time option specifies a start query time to the
DHCPv4 server. If specified, only bindings that have changed on or
after the query-start-time should be included in the response to the
query.
The requestor MUST determine the query-start-time using lease
information it has received from the DHCPv4 server. This MUST be an
absolute time in the DHCPv4 server's context (see Section 7.4).
Typically (though this is not a requirement), the query-start-time
option will contain the value most recently received in a base-time
option by the requestor, as this will indicate the last successful
communication with the DHCP server.
Kinnear, et al. Standards Track [Page 15]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
This MUST be an absolute time.
This is an unsigned integer in network byte order.
The code for this option is 154. The length of this option is 4
octets.
DHCPv4 Server
Code Len query-start-time
+-----+-----+-----+-----+-----+-----+
| 154 | 4 | t1 | t2 | t3 | t4 |
+-----+-----+-----+-----+-----+-----+
6.2.6. query-end-time
The query-end-time option specifies an end query time to the DHCPv4
server. If specified, only bindings that have changed on or before
the query-end-time should be included in the response to the query.
The requestor MUST determine the query-end-time based on lease
information it has received from the DHCPv4 server. This MUST be an
absolute time in the context of the DHCPv4 server.
In the absence of information to the contrary, the requestor SHOULD
assume that the time context of the DHCPv4 server is identical to the
time context of the requestor (see Section 7.4).
This is an unsigned integer in network byte order.
The code for this option is 155. The length of this option is 4
octets.
DHCPv4 Server
Code Len query-end-time
+-----+-----+-----+-----+-----+-----+
| 155 | 4 | t1 | t2 | t3 | t4 |
+-----+-----+-----+-----+-----+-----+
Kinnear, et al. Standards Track [Page 16]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
6.2.7. dhcp-state
The dhcp-state option allows greater detail to be returned than
allowed by the DHCPLEASEACTIVE and DHCPLEASEUNASSIGNED message types.
The code for this option is 156. The length of this option is 1
octet.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 156 | Length | State |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
156 The option code.
Length The option length, 1 octet.
State The state of the IP address.
Value State
----- -----
1 AVAILABLE Address is available to local DHCPv4 server
2 ACTIVE Address is assigned to a DHCPv4 client
3 EXPIRED Lease has expired
4 RELEASED Lease has been released by DHCPv4 client
5 ABANDONED Server or client flagged address as unusable
6 RESET Lease was freed by some external agent
7 REMOTE Address is available to a remote DHCPv4 server
8 TRANSITIONING Address is moving between states
Note that some of these states may be transient and may not appear in
normal use. A DHCPv4 server MUST implement at least the AVAILABLE
and ACTIVE states and SHOULD implement at least the ABANDONED and
RESET states.
Note the states AVAILABLE and REMOTE are relative to the current
server. An address that is available to the current server should
show AVAILABLE on that server, and if another server is involved with
that address as well, it should show as REMOTE on that other server.
The dhcp-state option SHOULD contain ACTIVE when it appears in a
DHCPLEASEACTIVE message. A DHCPv4 server MAY choose to not send a
dhcp-state option in a DHCPLEASEACTIVE message, and a requestor
SHOULD assume that the dhcp-state is ACTIVE if no dhcp-state option
appears in a DHCPLEASEACTIVE message.
Kinnear, et al. Standards Track [Page 17]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
The reference to local and remote relate to possible use in an
environment that includes multiple servers cooperating to provide an
increased availability solution. In this case, an IP address with
the state of AVAILABLE is available to the local server, while one
with the state of REMOTE is available to a remote server. Usually,
an IP address that is AVAILABLE on one server would be REMOTE on any
remote server. The TRANSITIONING state is also likely to be useful
in multiple server deployments, where sometimes one server must
interlock a state change with one or more other servers. Should a
Bulk Leasequery need to send information concerning the state of the
IP address during this period, it SHOULD use the TRANSITIONING state,
since the IP address is likely to be neither ACTIVE or AVAILABLE.
There is no requirement for the state of an IP address to transition
in a well-defined way from state to state. To put this another way,
you cannot draw a simple state transition graph for the states of an
IP address, and the requestor of a Leasequery MUST NOT depend on one
certain state always following a particular previous state. While a
state transition diagram can be drawn, it would be fully connected
and therefore conveys no useful information. Every state can (at
times) follow every other state.
6.2.8. data-source
The data-source option contains information about the source of the
data in a DHCPLEASEACTIVE or a DHCPLEASEUNASSIGNED message. It
SHOULD be used when there are two or more servers that might have
information about a particular IP address binding. Frequently, two
servers work together to provide an increased availability solution
for the DHCPv4 service, and in these cases, both servers will respond
to Bulk Leasequery requests for the same IP address. When one server
is working with another server and both may respond with information
about the same IP address, each server SHOULD return the data-source
option with the other information provided about the IP address.
The data contained in this option will allow an external process to
better discriminate between the information provided by each of the
servers servicing this IPv4 address.
Kinnear, et al. Standards Track [Page 18]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
The code for this option is 157. The length of this option is 1
octet.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 157 | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
157 The option code.
Length The option length, 1 octet.
Flags The source information for this message.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| UNA |R|
+-+-+-+-+-+-+-+-+
R: REMOTE flag
remote = 1
local = 0
UNA: UNASSIGNED
The REMOTE flag is used to indicate where the most recent change of
state (or other interesting change) concerning this IPv4 address took
place. If the value is local, then the change took place on the
server from which this message was transmitted. If the value is
remote, then the change took place on some other server and was made
known to the server from which this message was transmitted.
If this option was requested and it doesn't appear, the requestor
MUST consider that the data-source was local.
Unassigned bits MUST be ignored.
Kinnear, et al. Standards Track [Page 19]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
6.2.9. Virtual Subnet Selection Type and Information
All of the (sub-)options defined in [RFC6607] carry identical
payloads, consisting of a type and additional VSS (Virtual Subnet
Selection) information. The existing table is extended (see below)
with a new type 254 to allow specification of a type code that
indicates that all VPNs are to be used to process the Bulk
Leasequery.
Type VSS Information Format
----------------------------------------------------------
0 Network Virtual Terminal (NVT) ASCII VPN identifier
1 RFC 2685 VPN-ID
CHANGED -> 2-253 Unassigned
NEW -> 254 All VPNs (wildcard)
255 Global, default VPN
6.3. Connection and Transmission Parameters
DHCPv4 servers that support Bulk Leasequery SHOULD listen for
incoming TCP connections on the DHCPv4 server port 67.
Implementations MAY offer to make the incoming port configurable, but
port 67 MUST be the default. Requestors SHOULD make TCP connections
to port 67 and MAY offer to make the destination server port
configurable.
This section presents a table of values used to control Bulk
Leasequery behavior, including recommended defaults. Implementations
MAY make these values configurable. However, configuring too-small
timeout values may lead to harmful behavior both to this application
as well as to other traffic in the network. As a result, timeout
values smaller than the default values are NOT RECOMMENDED.
Parameter Default Description
--------------------------------------------------------------------
BULK_LQ_DATA_TIMEOUT 300 secs Bulk Leasequery data timeout
for both client and server
(see Sections 7 and 8)
BULK_LQ_MAX_CONNS 10 Max Bulk Leasequery TCP connections
at the server side (see Section 8.1)
Kinnear, et al. Standards Track [Page 20]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
7. Requestor Behavior
7.1. Connecting and General Processing
A requestor attempts to establish a TCP connection to a DHCPv4 server
in order to initiate a Leasequery exchange. If the attempt fails,
the requestor MAY retry.
If Bulk Leasequery is terminated prematurely by a DHCPLEASEQUERYDONE
with a status-code option with a status code of QueryTerminated or by
the failure of the connection over which it was being submitted, the
requestor MAY retry the request after the creation of a new
connection.
Messages from the DHCPv4 server come as multiple responses to a
single DHCPBULKLEASEQUERY message. Thus, each DHCPBULKLEASEQUERY
request MUST have an xid (transaction-id) unique on the connection on
which it is sent. All of the messages that come as a response to
that message will contain the same xid as the request. The xid
allows the data-streams of two different DHCPBULKLEASEQUERY requests
to be demultiplexed by the requestor.
7.2. Forming a Bulk Leasequery
Bulk Leasequery is designed to create a connection that will transfer
the state of some subset (or possibly all) of the IP address bindings
from the DHCPv4 server to the requestor. The DHCPv4 server will send
all of the requested IPv4 address bindings across this connection
with minimal delay after it receives the request. In this context,
"all IP address binding information" means information about all IPv4
addresses configured within the DHCPv4 server that meet the specified
query criteria. For some query criteria, this may include IP address
binding information for IP addresses that may not now have or ever
have had an association with a specific DHCPv4 client.
To form the Bulk query, a DHCPv4 request is constructed with a dhcp-
message-type of DHCPBULKLEASEQUERY. The query SHOULD have a dhcp-
parameter-request-list to inform the DHCPv4 server which DHCPv4
options are of interest to the requestor sending the
DHCPBULKLEASEQUERY message. The dhcp-parameter-request-list in a
DHCPBULKLEASEQUERY message SHOULD contain the codes for base-time,
dhcp-lease-time, start-time-of-state, and client-last-transaction-
time.
A DHCPBULKLEASEQUERY request is constructed of one primary query and
optionally one or more qualifiers for it.
Kinnear, et al. Standards Track [Page 21]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
The possible primary queries are listed below. Each
DHCPBULKLEASEQUERY request MUST contain only one of these primary
queries.
o Query by MAC address
In a Query by MAC address, the chaddr, htype, and hlen of the
DHCPv4 packet are filled in with the values requested.
o Query by Client-identifier
In a Query by Client-identifier, a Client-identifier option
containing the requested value is included in the
DHCPBULKLEASEQUERY request.
o Query by Remote ID
In a Query by Remote ID, a Remote ID sub-option containing the
requested value is included in the relay-agent-information option
of the DHCPBULKLEASEQUERY request.
o Query by Relay-ID
In a Query by Relay-ID, a Relay-ID sub-option [RFC6925] containing
the requested value is included in the relay-agent-information
option of the DHCPBULKLEASEQUERY request.
o Query for All Configured IP Addresses
A Query for All Configured IP addresses is signaled by the absence
of any other primary query.
There are three qualifiers that can be applied to any of the above
primary queries. These qualifiers can appear individually or
together in any combination, but only one of each can appear.
o Query Start Time
Inclusion of a query-start-time option specifies that only IP
address bindings that have changed on or after the time specified
in the query-start-time option should be returned.
o Query End Time
Inclusion of a query-end-time option specifies that only IP
address bindings that have changed on or before the time specified
in the query-end-time option should be returned.
Kinnear, et al. Standards Track [Page 22]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
o VPN-ID
If no VPN-ID option appears in the DHCPBULKLEASEQUERY, the default
(global) VPN is searched to satisfy the query specified by the
DHCPBULKLEASEQUERY. Using the VPN-ID option [RFC6607] allows the
requestor to specify a single VPN other than the default VPN. In
addition, the VPN-ID option has been extended as part of this
document to allow specification that all configured VPNs be
searched in order to satisfy the query specified in the
DHCPBULKLEASEQUERY.
In all cases, any message returned from a DHCPBULKLEASEQUERY
request containing information about an IP address for other than
the default (global) VPN MUST contain a VPN-ID option in the
message.
Use of the query-start-time or the query-end-time options or both can
serve to reduce the amount of data transferred over the TCP
connection by a considerable amount. Note that the times specified
in the query-start-time or query-end-time options are absolute times,
not durations offset from "now".
The TCP connection may become blocked or stop being writable while
the requestor is sending its query. Should this happen, the
implementation's behavior is controlled by the current value of
BULK_LQ_DATA_TIMEOUT. The default value is given elsewhere in this
document, and this value may be overridden by local configuration of
the operator.
If this situation is detected, the requestor SHOULD start a timer
using the current value of BULK_LQ_DATA_TIMEOUT. If that timer
expires, the requestor SHOULD terminate the connection. This timer
is completely independent of any TCP timeout established by the TCP
protocol connection.
7.3. Processing Bulk Replies
The requestor attempts to read a DHCPv4 Leasequery reply message from
the TCP connection.
The TCP connection may stop delivering reply data (i.e., the
connection stops being readable). Should this happen, the
implementation's behavior is controlled by the current value of
BULK_LQ_DATA_TIMEOUT. The default value is given elsewhere in this
document, and this value may be overridden by local configuration of
the operator.
Kinnear, et al. Standards Track [Page 23]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
If this situation is detected, the requestor SHOULD start a timer
using the current value of BULK_LQ_DATA_TIMEOUT. If that timer
expires, the requestor SHOULD terminate the connection.
A single Bulk Leasequery can, and usually will, result in a large
number of replies. The requestor MUST be prepared to receive more
than one reply with an xid matching a single DHCPBULKLEASEQUERY
message from a single DHCPv4 server. If the xid in the received
message does not match an outstanding DHCPBULKLEASEQUERY message, the
requestor MUST close the TCP connection.
If the requestor receives more data than it can process, it can
simply abort the connection and try again with a more specific
request. It can also simply read the TCP connection more slowly and
match the rate at which it can digest the information returned in the
Bulk Leasequery packets with the rate at which it reads those packets
from the TCP connection.
The DHCPv4 server MUST send a server-identifier option (option 54) in
the first response to any DHCPBULKLEASEQUERY message. The DHCPv4
server SHOULD NOT send server-identifier options in subsequent
responses to that DHCPBULKLEASEQUERY message. The requestor MUST
cache the server-identifier option from the first response and apply
it to any subsequent responses.
The response messages generated by a DHCPBULKLEASEQUERY request are:
o DHCPLEASEACTIVE
A Bulk Leasequery will generate DHCPLEASEACTIVE messages
containing binding data for bound IP addresses that match the
specified query criteria. The IP address that is bound to a
DHCPv4 client will appear in the ciaddr field of the
DHCPLEASEACTIVE message. The message may contain a non-zero
chaddr, htype, hlen, and possibly additional options.
o DHCPLEASEUNASSIGNED
Some queries will also generate DHCPLEASEUNASSIGNED messages for
IP addresses that match the query criteria. These messages
indicate that the IP address is managed by the DHCPv4 server but
is not currently bound to any DHCPv4 client. The IP address to
which this message refers will appear in the ciaddr field of the
DHCPLEASEUNASSIGNED message. A DHCPLEASEUNASSGINED message MAY
also contain information about the last DHCPv4 client that was
bound to this IP address. The message may contain a non-zero
chaddr, htype, hlen, and possibly additional options in this case.
Kinnear, et al. Standards Track [Page 24]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
o DHCPLEASEQUERYDONE
A response of DHCPLEASEQUERYDONE indicates that the server has
completed its response to the query and that no more messages will
be sent in response to the DHCPBULKLEASEQUERY. More details will
sometimes be available in the received status-code option in the
DHCPLEASEQUERYDONE message. If there is no status-code option in
the DHCPLEASEQUERYDONE message, then the query completed
successfully.
Note that a query that returned no data, that is, a
DHCPBULKLEASEQUERY request followed by a DHCPLEASEQUERYDONE
response, is considered a successful query in that no errors
occurred during the processing. It is not considered an error to
have no information to return to a DHCPBULKLEASEQUERY request.
The DHCPLEASEUNKNOWN message MUST NOT appear in a response to a Bulk
Leasequery.
The requestor MUST NOT assume that there is any inherent order in the
IP address binding information that is sent in response to a
DHCPBULKLEASEQUERY. While the base-time will tend to increase
monotonically (as it is the current time on the DHCPv4 server), the
actual time that any IP address binding information changed is
unrelated to the base-time.
The DHCPLEASEQUERYDONE message always ends a successful
DHCPBULKLEASEQUERY request and any unsuccessful DHCPBULKLEASEQUERY
requests not terminated by a dropped connection. After receiving a
DHCPLEASEQUERYDONE from a server, the requestor MAY close the TCP
connection to that server if no other DHCPBULKLEASEQUERY is
outstanding on that TCP connection.
The DHCPv4 Leasequery protocol [RFC4388] uses the associated-ip
option as an indicator that multiple bindings were present in
response to a single DHCPv4 client-based query. For Bulk Leasequery,
a separate message is returned for each binding, so the associated-ip
option is not used.
7.4. Processing Time Values in Leasequery Messages
Bulk Leasequery requests may be made to a DHCPv4 server whose
absolute time may not be synchronized with the local time of the
requestor. Thus, there are at least two time contexts in even the
simplest Bulk Leasequery response, and in the situation where
multiple DHCPv4 servers are queried, the situation becomes even more
complex.
Kinnear, et al. Standards Track [Page 25]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
If the requestor of a Bulk Leasequery is saving the data returned in
some form, it has a requirement to store a variety of time values;
some of these will be time in the context of the requestor, and some
will be time in the context of the DHCPv4 server.
When receiving a DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED message from
the DHCPv4 server, the message will contain a base-time option. The
time contained in this base-time option is in the context of the
DHCPv4 server. As such, it is an ideal time to save and use as input
to a DHCPBULKLEASEQUERY in the query-start-time or query-end-time
options, should the requestor ever need to issue a DHCPBULKLEASEQUERY
message using those options as part of a later query, since those
options require a time in the context of the DHCPv4 server.
In addition to saving the base-time for possible future use in a
query-start-time or query-end-time option, the base-time is used as
part of the conversion of the other times in the Leasequery message
to values that are meaningful in the context of the requestor. These
other time values are specified as a offset (duration) from the base-
time value and not as an absolute time.
In systems whose clocks are synchronized, perhaps using NTP, the
clock skew will usually be zero.
7.5. Querying Multiple Servers
A Bulk Leasequery requestor MAY be configured to attempt to connect
to and query from multiple DHCPv4 servers in parallel. The DHCPv4
Leasequery specification [RFC4388] includes a discussion about
reconciling binding data received from multiple DHCPv4 servers.
In addition, the algorithm in Section 7.6 should be used.
7.6. Making Sense out of Multiple Responses concerning a Single IPv4
Address
Any requestor of an Bulk Leasequery MUST be prepared for multiple
responses to arrive for a particular IPv4 address from multiple
different DHCPv4 servers. The following algorithm SHOULD be used to
decide if the information just received is more up to date (i.e.,
better) than the best existing information. In the discussion below,
the information that is received from a DHCPv4 server about a
particular IPv4 address is termed a "record". The times used in the
algorithm below SHOULD have been converted into the requestor's
context, and the time comparisons SHOULD be performed in a manner
consistent with the information in Section 7.4.
Kinnear, et al. Standards Track [Page 26]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
o If both the existing and the new record contain client-last-
transaction-time information, the record with the later client-
last-transaction-time is considered better.
o If one of the records contains client-last-transaction-time
information and the other one doesn't, then compare the client-
last-transaction-time in the record that contains it against the
other record's start-time-of-state. The record with the later
time is considered better.
o If neither record contains client-last-transaction-time
information, compare their start-time-of-state information. The
record with the later start-time-of-state is considered better.
o If none of the comparisons above yield a clear answer as to which
record is later, then compare the value of the REMOTE flag from
the data-source option for each record. If the values of the
REMOTE flag are different between the two records, the record with
the REMOTE flag value of local is considered better.
The above algorithm does not necessarily determine which record is
better. In the event that the algorithm is inconclusive with regard
to a record that was just received by the requestor, the requestor
SHOULD use additional information in the two records to make a
determination as to which record is better.
7.7. Multiple Queries to a Single Server over One Connection
Bulk Leasequery requestors may need to make multiple queries in order
to recover binding information. A requestor MAY use a single
connection to issue multiple queries to a server willing to support
them. Each query MUST have a unique xid.
A server SHOULD allow configuration of the number of queries that can
be processed simultaneously over a single connection. A server
SHOULD read the number of queries it is configured to process
simultaneously and only read any subsequent queries as current
queries are processed.
A server that is processing multiple queries simultaneously MUST NOT
block sending replies on new queries until all replies for the
existing query are complete. Requestors need to be aware that
replies for multiple queries may be interleaved within the stream of
reply messages. Requestors that are not able to process interleaved
replies (based on xid) MUST NOT send more than one query over a
single connection prior to the completion of the previous query.
Kinnear, et al. Standards Track [Page 27]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
Requestors should be aware that servers are not required to process
more than one query over a connection at a time (the limiting case
for the configuration described above) and that servers are likely to
limit the rate at which they process queries from any one requestor.
7.7.1. Example
This example illustrates what a series of queries and responses might
look like. This is only an example -- there is no requirement that
this sequence must be followed or that requestors or servers must
support parallel queries.
In the example session, the client sends four queries after
establishing a connection. Query 1 returns no results; query 2
returns 3 messages, and the stream of replies concludes before the
client issues any new query. Query 3 and query 4 overlap, and the
server interleaves its replies to those two queries.
Requestor Server
--------- ------
DHCPBULKLEASEQUERY xid 1 ----->
<----- DHCPLEASEQUERYDONE xid 1
DHCPBULKLEASEQUERY xid 2 ----->
<----- DHCPLEASEACTIVE xid 2
<----- DHCPLEASEACTIVE xid 2
<----- DHCPLEASEACTIVE xid 2
<----- DHCPLEASEQUERYDONE xid 2
DHCPBULKLEASEQUERY xid 3 ----->
DHCPBULKLEASEQUERY xid 4 ----->
<----- DHCPLEASEACTIVE xid 4
<----- DHCPLEASEACTIVE xid 4
<----- DHCPLEASEACTIVE xid 3
<----- DHCPLEASEACTIVE xid 4
<----- DHCPLEASEUNASSIGNED xid 3
<----- DHCPLEASEACTIVE xid 4
<----- DHCPLEASEACTIVE xid 3
<----- DHCPLEASEQUERYDONE xid 3
<----- DHCPLEASEACTIVE xid 4
<----- DHCPLEASEQUERYDONE xid 4
7.8. Closing Connections
If a requestor has no additional queries to send, or doesn't know if
it has additional queries to send or not, then it SHOULD close the
connection after receiving the DHCPLEASEQUERYDONE message for the
last outstanding query that it sent.
Kinnear, et al. Standards Track [Page 28]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
The requestor SHOULD close connections in a graceful manner and not
an abort. The requestor SHOULD NOT assume that the manner in which
the DHCP server closed a connection carries any special meaning.
Typically, the requestor is the entity that will close the
connection, as servers will often wait with an open connection in
case the requestor has additional queries.
If a server closes a connection with an exception condition, the
requestor SHOULD consider as valid any completely received
intermediate results, and the requestor MAY retry the Bulk Leasequery
operation.
8. Server Behavior
8.1. Accepting Connections
Servers that implement DHCPv4 Bulk Leasequery listen for incoming TCP
connections. Port numbers are discussed in Section 6.3. Servers
MUST be able to limit the number of concurrently accepted and active
connections. The value BULK_LQ_MAX_CONNS SHOULD be the default;
implementations MAY permit the value to be configurable. Connections
SHOULD be accepted and, if the number of connections is over
BULK_LQ_MAX_CONNS, they SHOULD be closed immediately.
Servers MAY restrict Bulk Leasequery connections and
DHCPBULKLEASEQUERY messages to certain requestors. Connections not
from permitted requestors SHOULD be closed immediately to avoid
server connection resource exhaustion. Servers MAY restrict some
requestors to certain query types. Servers MAY reply to queries that
are not permitted with the DHCPLEASEQUERYDONE message with a status-
code option status of NotAllowed or MAY simply close the connection.
If the TCP connection becomes blocked while the server is accepting a
connection or reading a query, it SHOULD be prepared to terminate the
connection after a BULK_LQ_DATA_TIMEOUT. We make this recommendation
to allow servers to control the period of time they are willing to
wait before abandoning an inactive connection, independent of the TCP
implementations they may be using.
8.2. Replying to a Bulk Leasequery
If the connection becomes blocked while the server is attempting to
send reply messages, the server SHOULD be prepared to terminate the
TCP connection after a BULK_LQ_DATA_TIMEOUT.
Kinnear, et al. Standards Track [Page 29]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
Every Bulk Leasequery request MUST be terminated by sending a final
DHCPLEASEQUERYDONE message if such a message can be sent. The
DHCPLEASEQUERYDONE message MUST have a status-code option status if
the termination was other than successful, and SHOULD NOT contain a
status-code option status if the termination was successful.
If the DHCPv4 server encounters an error during processing of the
DHCPBULKLEASEQUERY message, either during initial processing or later
during the message processing, it SHOULD send a DHCPLEASEQUERYDONE
containing a status-code option. It MAY close the connection after
this error is signaled, but that is not required.
If the server does not find any bindings satisfying a query, it MUST
send a DHCPLEASEQUERYDONE. It SHOULD NOT include a status-code
option with a Success status unless there is a useful string to
include in the status-code option. Otherwise, the server sends each
binding's data in a DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED message.
The response to a DHCPBULKLEASEQUERY may involve examination of
multiple DHCPv4 IP address bindings maintained by the DHCPv4 server.
The Bulk Leasequery protocol does not require any ordering of the IP
addresses returned in DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED
messages.
When responding to a DHCPBULKLEASEQUERY message, the DHCPv4 server
MUST NOT send more than one message for each applicable IP address,
even if the state of some of those IP addresses changes during the
processing of the message. Updates to such IP address state are
already handled by normal protocol processing, so no special effort
is needed here.
If the ciaddr, yiaddr, or siaddr is non-zero in a DHCPBULKLEASEQUERY
request, the request must be terminated immediately by a
DHCPLEASEQUERYDONE message with a status-code option status of
MalformedQuery.
Any DHCPBULKLEASEQUERY that has more than one of the following
primary query types specified MUST be terminated immediately by a
DHCPLEASEQUERYDONE message with a status-code option status code of
NotAllowed.
The allowable queries in a DHCPBULKLEASEQUERY message are processed
as follows. Note that the descriptions of the primary queries below
must be constrained by the actions of any of the three qualifiers
described subsequently as well.
Kinnear, et al. Standards Track [Page 30]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
The following table discusses how to process the various queries.
For information on how to identify the query, see the information in
Section 7.2.
o Query by MAC address
Every IP address that has a current binding to a DHCPv4 client
matching the chaddr, htype, and hlen in the DHCPBULKLEASEQUERY
request MUST be returned in a DHCPLEASEACTIVE message.
o Query by Client-identifier
Every IP address that has a current binding to a DHCPv4 client
matching the Client-identifier option in the DHCPBULKLEASEQUERY
request MUST be returned in a DHCPLEASEACTIVE message.
o Query by Remote ID
Every IP address that has a current binding to a DHCPv4 client
matching the Remote ID sub-option of the relay-agent-information
option in the DHCPBULKLEASEQUERY request MUST be returned in a
DHCPLEASEACTIVE message.
o Query by Relay-ID
Every IP address that has a current binding to a DHCPv4 client
matching the Relay-ID sub-option of the relay-agent-information
option in the DHCPBULKLEASEQUERY request MUST be returned in a
DHCPLEASEACTIVE message.
o Query for All Configured IP Addresses
A Query for All Configured IP addresses is signaled by the absence
of any other primary query. That is, if there is no value in the
chaddr, hlen, htype, no Client-identifier option, and no Remote ID
sub-option or Relay-ID sub-option of the relay-agent-information
option, then the request is a query for information concerning all
configured IP addresses. In this case, every configured IP
address that has a current binding to a DHCPv4 client MUST be
returned in a DHCPLEASEACTIVE message. In addition, every
configured IP address that does not have a current binding to a
DHCPv4 client MUST be returned in a DHCPLEASEUNASSIGNED message.
In this form of query, each configured IP address MUST be returned
at most one time. In the absence of qualifiers restricting the
number of IP addresses returned, every configured IP address MUST
be returned exactly once.
Kinnear, et al. Standards Track [Page 31]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
There are three qualifiers that can be applied to any of the above
primary queries. These qualifiers can appear individually or
together in any combination, but only one of each can appear.
o Query Start Time
If a query-start-time option appears in the DHCPBULKLEASEQUERY
request, only IP address bindings that have changed on or after
the time specified in the query-start-time option should be
returned.
o Query End Time
If a query-end-time option appears in the DHCPBULKLEASEQUERY
request, only IP address bindings that have changed on or before
the time specified in the query-end-time option should be
returned.
o VPN-ID
If no VPN-ID option appears in the DHCPBULKLEASEQUERY, the default
(global) VPN is used to satisfy the query. A VPN-ID option
[RFC6607] value other than the wildcard value (254) allows the
requestor to specify a single VPN other than the default VPN. In
addition, the VPN-ID option has been extended as part of this
document to allow specification of a type 254, which indicates
that all configured VPNs be searched in order to satisfy the
primary query.
In all cases, if the information returned in a DHCPLEASEACTIVE or
DHCPLEASEUNASSIGNED message is for a VPN other than the default
(global) VPN, a VPN-ID option MUST appear in the packet.
The query-start-time and query-end-time qualifiers are used to
constrain the amount of data returned by a Bulk Leasequery request by
returning only IP addresses whose address bindings have changed in
some way during the time window specified by the query-start-time and
query-end-time.
A DHCPv4 server SHOULD consider an address binding to have changed
during a specified time window if either the client-last-
transaction-time or the start-time-of-state of the address binding
changed during that time window.
The DHCPv4 server MAY return address binding data in any order, as
long as binding information for any given IP address is not repeated.
When all binding data for a given DHCPBULKLEASEQUERY has been sent,
the DHCPv4 server MUST send a DHCPBULKLEASEQUERYDONE message.
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RFC 6926 DHCPv4 Bulk Leasequery April 2013
8.3. Building a Single Reply for Bulk Leasequery
The DHCPv4 Leasequery specification [RFC4388] describes the initial
construction of DHCPLEASEQUERY reply messages using the
DHCPLEASEACTIVE and DHCPLEASEUNASSIGNED message types in Section
6.4.2. All of the reply messages in Bulk Leasequery are similar to
the reply messages for an IP address query. Message transmission and
framing for TCP are described in this document in Section 6.1.
[RFC2131] and [RFC4388] specify that every response message MUST
contain the server-identifier option. However, that option will be
the same for every response from a particular DHCPBULKLEASEQUERY
request. Thus, the DHCPv4 server MUST include the server-identifier
option in the first message sent in response to a DHCPBULKLEASEQUERY.
It SHOULD NOT include the server-identifier option in later messages.
The message type of DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED is based
on the value of the dhcp-state option. If the dhcp-state option
value is ACTIVE, then the message type is DHCPLEASEACTIVE; otherwise,
the message type is DHCPLEASEUNASSIGNED.
In addition to the basic message construction described in [RFC4388],
the following guidelines exist:
1. If the dhcp-state option code appears in the dhcp-parameter-
request-list, the DHCPv4 server SHOULD include a dhcp-state
option whose value corresponds most closely to the state held by
the DHCPv4 server for the IP address associated with this reply.
If the state is ACTIVE and the message being returned is
DHCPLEASEACTIVE, then the DHCPv4 server MAY choose to not send
the dhcp-state option. The requestor SHOULD assume that any
DHCPLEASEACTIVE message arriving without a requested dhcp-state
option has a dhcp-state of ACTIVE.
2. If the base-time option code appears in the dhcp-parameter-
request-list, the DHCPv4 server MUST include a base-time option,
which is the current time in the DHCPv4 server's context and the
time from which the start-time-of-state, dhcp-lease-time, client-
last-transaction-time, and other duration-style times are based
upon.
3. If the start-time-of-state option code appears in the dhcp-
parameter-request-list, the DHCPv4 server MUST include a start-
time-of-state option whose value represents the time at which the
dhcp-state option's state became valid.
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RFC 6926 DHCPv4 Bulk Leasequery April 2013
4. If the dhcp-lease-time option code appears in the dhcp-
parameter-request-list, the DHCPv4 server MUST include a dhcp-
lease-time option for any state that has a timeout value
associated with it.
5. If the data-source option code appears in the dhcp-parameter-
request-list, the DHCPv4 server MUST include the data-source
option in any situation where any of the bits would be non-zero.
Thus, in the absence of the data-source option, the assumption is
that all of the flags are zero.
6. If the client-last-transaction-time option code appears in the
dhcp-parameter-request-list, the DHCPv4 server MUST include the
client-last-transaction-time option in any situation where the
information is available.
7. If there is a dhcp-parameter-request-list in the initial
DHCPBULKLEASEQUERY request, then it should be used for all of the
replies generated by that request. Some options can be sent from
a DHCPv4 client to the server or from the DHCPv4 server to a
DHCPv4 client. Option 125 is such an option. If the option code
for one of these options appears in the dhcp-parameter-request-
list, it SHOULD result in returning the value of the option sent
by the DHCPv4 client to the server if one exists.
Note that there may be other requirements for a reply to a
DHCPBULKLEASEQUERY request, as discussed in Section 8.2.
8.4. Multiple or Parallel Queries
As discussed in Section 7.3, requestors may want to use a connection
that has already been established when they need to make additional
queries. Servers SHOULD support reading and processing multiple
queries from a single connection and SHOULD allow configuration of
the number of simultaneous queries it may process. A server MUST NOT
read more query messages from a connection than it is prepared to
process simultaneously.
This SHOULD be a feature that is administratively controlled.
Servers SHOULD offer configuration that limits the number of
simultaneous queries permitted from any one requestor, in order to
control resource use if there are multiple requestors seeking
service.
Kinnear, et al. Standards Track [Page 34]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
8.5. Closing Connections
The DHCPv4 server SHOULD close connections in a graceful manner and
not abort the connection. The DHCPv4 server SHOULD NOT assume that
the manner in which the requestor closed a connection carries any
special meaning.
Typically, the DHCPv4 server will only close the connection after
some form of an exception or a timeout on the connection.
Using a timer to detect when a connection is idle and then closing
that connection is designed to protect the DHCPv4 server from
consuming unnecessary resources.
The DHCPv4 server should start a timer for BULK_LQ_DATA_TIMEOUT
seconds for a particular connection after it sends a
DHCPLEASEQUERYDONE message over that connection if there is no
current query outstanding for that connection. It should restart
this timer if a query arrives over that connection. If the timer
expires, the DHCPv4 server should close the connection.
The server MUST close its end of the TCP connection if it encounters
an error sending data on the connection. The server MUST close its
end of the TCP connection if it finds that it has to abort an in-
process request. A server aborting an in-process request SHOULD
attempt to signal that to its requestors by using the QueryTerminated
status code in the status-code option in a DHCPLEASEQUERYDONE
message, including a message string indicating details of the reason
for the abort. If the connection is closed for any reason, all of
the data flows associated with any currently outstanding
DHCPBULKLEASEQUERY messages will be terminated.
If the server detects that the requesting end of the connection has
been closed, the server MUST close its end of the connection.
9. Security Considerations
The Security Considerations section of [RFC2131] details the general
threats to DHCPv4. The DHCPv4 Leasequery specification [RFC4388]
describes recommendations for the Leasequery protocol, especially
with regard to authentication of LEASEQUERY messages, mitigation of
packet-flooding DoS attacks, and restriction to trusted requestors.
The use of TCP introduces some additional concerns. Attacks that
attempt to exhaust the DHCPv4 server's available TCP connection
resources, such as SYN flooding attacks, can compromise the ability
of legitimate requestors to receive service. Malicious requestors
who succeed in establishing connections but who then send invalid
Kinnear, et al. Standards Track [Page 35]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
queries, partial queries, or no queries at all can also exhaust a
server's pool of available connections. We recommend that servers
offer configuration to limit the sources of incoming connections,
that they limit the number of accepted connections and the number of
in-process queries from any one connection, and that they limit the
period of time during which an idle connection will be left open.
There are two specific issues regarding Bulk Leasequery security that
deserve explicit mention. The first is preventing information that
Bulk Leasequery can provide from reaching clients who are not
authorized to receive such information. The second is ensuring that
authorized clients of the Bulk Leasequery capability receive accurate
information from the server (and that this information is not
disrupted in transit).
To prevent information leakage to unauthorized clients, servers
SHOULD restrict Bulk Leasequery connections and DHCPBULKLEASEQUERY
messages to certain requestors, either through explicit configuration
of the server itself or by employing external network elements to
provide such restrictions. In particular, the typical DHCPv4 client
SHOULD NOT be allowed to receive a response to a Bulk Leasequery
request, and some technique MUST exist to allow prevention of such
access in any environment where Bulk Leasequery is deployed.
Connections not from permitted requestors SHOULD be closed
immediately to avoid server connection resource exhaustion or
alternatively, simply not be allowed to reach the server at all.
Servers SHOULD have the capability to restrict certain requestors to
certain query types. Servers MAY reply to queries that are not
permitted with the DHCPLEASEQUERYDONE message with a status-code
option status of NotAllowed or MAY simply close the connection.
To prevent disruption and malicious corruption of Bulk Leasequery
data flows between the server and authorized clients, these data
flows SHOULD transit only secured networks. These data flows are
typically infrastructure oriented, and there is usually no reason to
have them flowing over networks where such attacks are likely. In
the rare cases where these data flows might need to be sent through
unsecured networks, they MUST be sent over connections secured
through means external to the DHCPv4/DHCPv6 server and its client(s)
(e.g., through VPNs).
Authentication for DHCP messages [RFC3118] MUST NOT be used to
attempt to secure transmission of the messages described in this
document. In particular, the message framing would not be protected
by using the mechanisms described in [RFC3118] (which was designed
only with UDP transport in mind).
Kinnear, et al. Standards Track [Page 36]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
10. IANA Considerations
IANA has assigned the following new DHCPv4 option codes from the
registry "BOOTP Vendor Extensions and DHCP Options" maintained at
http://www.iana.org/assignments/bootp-dhcp-parameters.
1. An option code of 151 for status-code.
2. An option code of 152 for base-time.
3. An option code of 153 for start-time-of-state.
4. An option code of 154 for query-start-time.
5. An option code of 155 for query-end-time.
6. An option code of 156 for dhcp-state.
7. An option code of 157 for data-source.
IANA has assigned the following new DHCP message types from the
registry "DHCP Message Type 53 Values" maintained at
http://www.iana.org/assignments/bootp-dhcp-parameters.
1. A dhcp-message-type of 14 for DHCPBULKLEASEQUERY.
2. A dhcp-message-type of 15 for DHCPLEASEQUERYDONE.
IANA has created a new registry on the same assignments page, titled
"DHCP State 156 Values" (where 156 corresponds to the assigned value
of the dhcp-state option above). This registry has the following
initial values:
State
-----
1 AVAILABLE
2 ACTIVE
3 EXPIRED
4 RELEASED
5 ABANDONED
6 RESET
7 REMOTE
8 TRANSITIONING
New values for this namespace may only be defined by IETF Review, as
described in [RFC5226].
Kinnear, et al. Standards Track [Page 37]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
IANA has created a new registry on the same assignments page, titled
"DHCP Status Code 151 Values" (where 151 corresponds to the assigned
value of the status-code option above). This registry has the
following initial values:
Name status-code
---- -----------
Success 000
UnspecFail 001
QueryTerminated 002
MalformedQuery 003
NotAllowed 004
New values for this namespace may only be defined by IETF Review, as
described in [RFC5226].
IANA has revised the registry "VSS Type Options" created by [RFC6607]
in the overall area "Dynamic Host Configuration Protocol (DHCP) and
Bootstrap Protocol (BOOTP) Parameters". It has been revised to
appear as follows. Note that the number range for "Unassigned" has
changed, and a new line for "All VPNs (wildcard)" was added.
Type VSS Information Format
------------------------------------------------------------
0 Network Virtual Terminal (NVT) ASCII VPN identifier
1 RFC 2685 VPN-ID
2-253 Unassigned
254 All VPNs (wildcard)
255 Global, default VPN
11. Acknowledgements
Significant text as well as important ideas were borrowed in whole or
in part from "DHCPv6 Bulk Leasequery" [RFC5460], written by Mark
Stapp. Further suggestions and improvements were made by
participants in the DHC Working Group, including Alfred Hoenes.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
Kinnear, et al. Standards Track [Page 38]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC
3046, January 2001.
[RFC3118] Droms, R., Ed., and W. Arbaugh, Ed., "Authentication for
DHCP Messages", RFC 3118, June 2001.
[RFC4388] Woundy, R. and K. Kinnear, "Dynamic Host Configuration
Protocol (DHCP) Leasequery", RFC 4388, February 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",
BCP 153, RFC 5735, January 2010.
[RFC6607] Kinnear, K., Johnson, R., and M. Stapp, "Virtual Subnet
Selection Options for DHCPv4 and DHCPv6", RFC 6607, April
2012.
[RFC6925] Joshi, B., Desetti, R., and M. Stapp, "The DHCPv4 Relay
Agent Identifier Sub-Option", RFC 6925, April 2013.
12.2. Informative References
[RFC951] Croft, W. and J. Gilmore, "Bootstrap Protocol", RFC 951,
September 1985.
[RFC1542] Wimer, W., "Clarifications and Extensions for the
Bootstrap Protocol", RFC 1542, October 1993.
[RFC4614] Duke, M., Braden, R., Eddy, W., and E. Blanton, "A Roadmap
for Transmission Control Protocol (TCP) Specification
Documents", RFC 4614, September 2006.
[RFC5460] Stapp, M., "DHCPv6 Bulk Leasequery", RFC 5460, February
2009.
Kinnear, et al. Standards Track [Page 39]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
Authors' Addresses
Kim Kinnear
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, Massachusetts 01719
USA
Phone: (978) 936-0000
EMail: kkinnear@cisco.com
Mark Stapp
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, Massachusetts 01719
USA
Phone: (978) 936-0000
EMail: mjs@cisco.com
D.T.V Ramakrishna Rao
Infosys Ltd.
44 Electronics City, Hosur Road
Bangalore 560 100
India
EMail: ramakrishnadtv@infosys.com
URI: http://www.infosys.com/
Bharat Joshi
Infosys Ltd.
44 Electronics City, Hosur Road
Bangalore 560 100
India
EMail: bharat_joshi@infosys.com
URI: http://www.infosys.com/
Neil Russell
Sea Street Technologies Inc.
EMail: neil.e.russell@gmail.com
Kinnear, et al. Standards Track [Page 40]
RFC 6926 DHCPv4 Bulk Leasequery April 2013
Pavan Kurapati
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
USA
EMail: kurapati@juniper.net
URI: http://www.juniper.net/
Bernie Volz
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, Massachusetts 01719
USA
Phone: (978) 936-0000
EMail: volz@cisco.com
Kinnear, et al. Standards Track [Page 41]