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Network Working Group J. Kempf, Ed.
Request for Comments: 4831 DoCoMo USA Labs
Category: Informational April 2007
Goals for Network-Based Localized Mobility Management (NETLMM)
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
In this document, design goals for a network-based localized mobility
management (NETLMM) protocol are discussed.
Table of Contents
1. Introduction ....................................................2
1.1. Terminology ................................................2
2. NETLMM Functional Architecture ..................................3
3. Goals for the NETLMM Protocol ...................................3
3.1. Goal 1: Handover Performance Improvement ...................4
3.2. Goal 2: Reduction in Handover-Related Signaling Volume .....5
3.3. Goal 3: Location Privacy ...................................6
3.4. Goal 4: Limit Overhead in the Network ......................7
3.5. Goal 5: Simplify Mobile Node Mobility Management
Security by Deriving from IP Network Access and/or IP
Movement Detection Security ................................7
3.6. Goal 6: Link Technology Agnostic ...........................8
3.7. Goal 7: Support for Unmodified Mobile Nodes ................8
3.8. Goal 8: Support for IPv4 and IPv6 ..........................9
3.9. Goal 9: Reuse of Existing Protocols Where Sensible ........10
3.10. Goal 10: Localized Mobility Management
Independent of Global Mobility Management ................10
3.11. Goal 11: Configurable Data Plane Forwarding
between Local Mobility Anchor and Mobile Access Gateway ..11
4. Security Considerations ........................................11
5. Acknowledgements ...............................................11
6. Normative References ...........................................12
7. Informative References .........................................12
8. Contributors ...................................................13
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1. Introduction
In [1], the basic problems that occur when a global mobility protocol
is used for managing local mobility are described, and two currently
used approaches to localized mobility management -- the host-based
approach that is used by most IETF protocols, and the proprietary
Wireless LAN (WLAN) switch approach used between WLAN switches in
different subnets -- are examined. The conclusion from the problem
statement document is that none of the approaches has a complete
solution to the problem. While the WLAN switch approach is most
convenient for network operators and users because it requires no
software on the mobile node other than the standard drivers for WiFi,
the proprietary nature limits interoperability, and the restriction
to a single last-hop link type and wired backhaul link type restricts
scalability. The IETF host-based protocols require host software
stack changes that may not be compatible with all global mobility
protocols. They also require specialized and complex security
transactions with the network that may limit deployability. The
conclusion is that a localized mobility management protocol that is
network based and requires no software on the host for localized
mobility management is desirable.
This document develops a brief functional architecture and detailed
goals for a network-based localized mobility management protocol
(NETLMM). Section 2 describes the functional architecture of NETLMM.
In Section 3, a list of goals that is desirable in the NETLMM
protocol is presented. Section 4 briefly outlines Security
Considerations. More discussion of security can be found in the
threat analysis document [2].
1.1. Terminology
Mobility terminology in this document follows that in RFC 3753 [10]
and in [1]. In addition, the following terms are related to the
functional architecture described in Section 2:
Localized Mobility Management Domain
An Access Network in the sense defined in [1] in which mobility is
handled by the NETLMM protocol.
Mobile Access Gateway
A Mobile Access Gateway (MAG) is a functional network element that
terminates a specific edge link and tracks mobile node IP-level
mobility between edge links, through NETLMM signaling with the
Localized Mobility Anchor. The MAG also terminates host routed
data traffic from the Localized Mobility Anchor for mobile nodes
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currently located within the edge link under the MAG's control,
and forwards data traffic from mobile nodes on the edge link under
its control to the Localized Mobility Anchor.
Local Mobility Anchor
A Local Mobility Anchor (LMA) is a router that maintains a
collection of host routes and associated forwarding information
for mobile nodes within a localized mobility management domain
under its control. Together with the MAGs associated with it, the
LMA uses the NETLMM protocol to manage IP node mobility within the
localized mobility management domain. Routing of mobile node data
traffic is anchored at the LMA as the mobile node moves around
within the localized mobility management domain.
2. NETLMM Functional Architecture
The NETLMM architecture consists of the following components.
Localized Mobility Anchors (LMAs) within the backbone network
maintain a collection of routes for individual mobile nodes within
the localized mobility management domain. The routes point to the
Mobile Access Gateways (MAGs) managing the links on which the mobile
nodes currently are located. Packets for a mobile node are routed to
and from the mobile node through tunnels between the LMA and MAG.
When a mobile node moves from one link to another, the MAG sends a
route update to the LMA. While some mobile node involvement is
necessary and expected for generic mobility functions such as
movement detection and to inform the MAG about mobile node movement,
no specific mobile-node-to-network protocol will be required for
localized mobility management itself. Host stack involvement in
mobility management is thereby limited to generic mobility functions
at the IP layer, and no specialized localized mobility management
software is required.
3. Goals for the NETLMM Protocol
Section 2 of [1] describes three problems with using a global
mobility management protocol for localized mobility management. Any
localized mobility management protocol must naturally address these
three problems. In addition, the side effects of introducing such a
solution into the network need to be limited. In this section, we
address goals for NETLMM, including both solving the basic problems
(Goals 1, 2, and 3) and limiting the side effects (Goals 4+).
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Some basic goals of all IETF protocols are not discussed in detail
here, but any solution is expected to satisfy them. These goals are
fault tolerance, robustness, interoperability, scalability, and
minimal specialized network equipment. A good discussion of their
applicability to IETF protocols can be found in [4].
Out of scope for the initial goals discussion are Quality of Service
(QoS) and dormant mode/paging. While these are important functions
for mobile nodes, they are not part of the base localized mobility
management problem. In addition, mobility between localized mobility
management domains is not covered here. It is assumed that this is
covered by the global mobility management protocols.
3.1. Goal 1: Handover Performance Improvement
Handover packet loss occurs because there is usually latency between
when the link handover starts and when the IP subnet configuration
and global mobility management signaling completes. During this
time, the mobile node is unreachable at its former topological
location on the old link where correspondents are sending packets.
Such misrouted packets are dropped. This aspect of handover
performance optimization has been the subject of much work, both in
other Standards Development Organizations (SDOs) and in the IETF, in
order to reduce the latency in IP handover. Many solutions to this
problem have been proposed at the link layer and at the IP layer.
One aspect of this goal for localized mobility management is that the
processing delay for changing the forwarding after handover must
approach as closely as possible the sum of the delay associated with
link-layer handover and the delay required for active IP-layer
movement detection, in order to avoid excessive packet loss.
Ideally, if network-side link-layer support is available for handling
movement detection prior to link handover or as part of the link
handover process, the routing update should complete within the time
required for link handover. This delay is difficult to quantify, but
for voice traffic, the entire handover delay, including Layer 2
handover time and IP handover time should be between 40-70 ms to
avoid any degradation in call quality. Of course, if the link-layer
handover latency is too high, sufficient IP-layer handover
performance for good real-time service cannot be matched.
A goal of the NETLMM protocol -- in networks where the link-layer
handover latency allows it -- is to reduce the amount of latency in
IP handover, so that the combined IP-layer and link-layer handover
latency is less than 70 ms.
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3.2. Goal 2: Reduction in Handover-Related Signaling Volume
Considering Mobile IPv6 [9] as the global mobility protocol (other
mobility protocols require about the same or somewhat less), if a
mobile node using address autoconfiguration is required to
reconfigure on every move between links, the following signaling must
be performed:
1) Link-layer signaling required for handover and reauthentication.
For example, in 802.11 [7], this is the Reassociate message
together with 802.1x [8] reauthentication using EAP.
2) Active IP-level movement detection, including router reachability.
The Detecting Network Attachment (DNA) protocol [5] uses Router
Solicitation/Router Advertisement for this purpose. In addition,
if SEcure Neighbor Discovery (SEND) [3] is used and the mobile
node does not have a certificate cached for the router, the mobile
node must use Certification Path Solicitation/Certification Path
Advertisement to obtain a certification path.
3) Two Multicast Listener Discovery (MLD) [14] REPORT messages, one
for each of the solicited node multicast addresses corresponding
to the link local address and the global address.
4) Two Neighbor Solicitation (NS) messages for duplicate address
detection, one for the link local address and one for the global
address. If the addresses are unique, no response will be
forthcoming.
5) Two NS messages from the router for address resolution of the link
local and global addresses, and two Neighbor Advertisement
messages in response from the mobile node.
6) Binding Update/Binding Acknowledgement between the mobile node and
home agent to update the care of address binding.
7) Return routability signaling between the correspondent node and
mobile node to establish the binding key, consisting of one Home
Test Init/Home Test and Care of Test Init/Care of Test.
8) Binding Update/Binding Acknowledgement between the correspondent
node and mobile node for route optimization.
Note that Steps 1-2 may be necessary, even for intra-link mobility,
if the last-hop link protocol doesn't provide much help for IP
handover. Steps 3-5 will be different if stateful address
configuration is used, since additional messages are required to
obtain the address. Steps 6-8 are only necessary when Mobile IPv6 is
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used. The result is approximately 18 messages at the IP level, where
the exact number depends on various specific factors, such as whether
or not the mobile node has a router certificate cached before a
mobile node can be ensured that it is established on a link and has
full IP connectivity. In addition to handover related signaling, if
the mobile node performs Mobile IPv6 route optimization, it may be
required to renew its return routability key periodically (on the
order of every 7 minutes), even if it is not moving, resulting in
additional signaling.
The signaling required has a large impact on the performance of
handover, impacting Goal 1. Perhaps more importantly, the aggregate
impact from many mobile nodes of such signaling on expensive shared
links (such as wireless where the capacity of the link cannot easily
be expanded) can result in reduced last-hop link capacity for data
traffic. Additionally, in links where the end user is charged for IP
traffic, IP signaling is not without cost.
To address the issue of signaling impact described above, the goal is
that handover signaling volume from the mobile node to the network
should be no more than what is needed for the mobile node to perform
secure IP-level movement detection, in cases where no link-layer
support exists. Furthermore, NETLMM should not introduce any
additional signaling during handover beyond what is required for IP-
level movement detection. If link-layer support exists for IP-level
movement detection, the mobile node may not need to perform any
additional IP-level signaling after link-layer handover.
3.3. Goal 3: Location Privacy
In any IP network, there is a threat that an attacker can determine
the physical location of a network node from the node's topological
location. Depending on how an operator deploys their network, an
operator may choose to assign subnet coverage in a way that is
tightly bound to geography at some timescale, or it may choose to
assign it in ways in which the threat of someone finding a node
physically based on its IP address is smaller. Allowing the L2
attachment and L3 address to be less tightly bound is one tool for
reducing this threat to location privacy.
Mobility introduces an additional threat. An attacker can track a
mobile node's geographical location in real-time, if the victim
mobile node must change its IP address as it moves from one subnet to
another through the covered geographical area. If the granularity of
the mapping between the IP subnets and geographical area is small for
the particular link type in use, the attacker can potentially
assemble enough information to find the victim in real time.
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In order to reduce the risk from location privacy compromises as a
result of IP address changes, the goal for NETLMM is to remove the
need to change IP address as a mobile node moves across links in an
access network. Keeping the IP address fixed over a large
geographical region fuzzes out the resolution of the mapping between
the IP subnets and geographical area, regardless of how small the
natural deployment granularity may be. This reduces the chance that
the attacker can deduce the precise geographic location of the mobile
node.
3.4. Goal 4: Limit Overhead in the Network
Access networks, including both the wired and wireless parts, tend to
have somewhat stronger bandwidth and router processing constraints
than the backbone. In the wired part of the network, these
constraints are a function of the cost of laying fiber or wiring to
the wireless access points in a widely dispersed geographic area. In
the wireless part of the network, these constraints are due to the
limitation on the number of bits per Hertz imposed by the physical
layer protocol. Therefore, any solutions for localized mobility
management should minimize overhead within the access network.
3.5. Goal 5: Simplify Mobile Node Mobility Management Security by
Deriving from IP Network Access and/or IP Movement Detection
Security
Localized mobility management protocols that have host involvement
may require an additional security association between the mobile
node and the mobility anchor, and establishing this security
association may require additional signaling between the mobile node
and the mobility anchor (see [13] for an example). The additional
security association requires extra signaling and therefore extra
time to negotiate. Reducing the complexity of mobile-node-to-network
security for localized mobility management can therefore reduce
barriers to deployment and improve responsiveness. Naturally, such
simplification must not come at the expense of maintaining strong
security guarantees for both the network and mobile node.
In NETLMM, the network (specifically, the MAG) derives the occurrence
of a mobility event, requiring a routing update for a mobile node
from link-layer handover signaling, or IP-layer movement detection
signaling from the mobile node. This information is used to update
routing for the mobile node at the LMA. The handover, or movement
detection signaling, must provide the network with proper
authentication and authorization so that the network can definitively
identify the mobile node and determine its authorization. The
authorization may be at the IP level -- for example, using something
like SEND [3] to secure IP movement detection signaling -- or it at
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the link level. Proper authentication and authorization must be
implemented on link-layer handover signaling and/or IP-level movement
detection signaling in order for the MAG to securely deduce mobile
node movement events. Security threats to the NETLMM protocol are
discussed in [2].
The goal is that security for NETLMM mobile node mobility management
should derive from IP network access and/or IP movement detection
security, such as SEND or network access authentication, and not
require any additional security associations or additional signaling
between the mobile node and the network.
3.6. Goal 6: Link Technology Agnostic
The number of wireless link technologies available is growing, and
the growth seems unlikely to slow down. Since the standardization of
a wireless link physical and medium access control layers is a time-
consuming process, reducing the amount of work necessary to interface
a particular wireless link technology to an IP network is necessary.
When the last-hop link is a wireless link, a localized mobility
management solution should ideally require minimal work to interface
with a new wireless link technology.
In addition, an edge mobility solution should provide support for
multiple wireless link technologies. It is not required that the
localized mobility management solution support handover from one
wireless link technology to another without a change in the IP
address, but this possibility should not be precluded.
The goal is that the localized mobility management protocol should
not use any wireless link specific information for basic routing
management, though it may be used for other purposes, such as
securely identifying a mobile node.
3.7. Goal 7: Support for Unmodified Mobile Nodes
In the WLAN switching market, no modification of the software on the
mobile node is required to achieve localized mobility management.
Being able to accommodate unmodified mobile nodes enables a service
provider to offer service to as many customers as possible, the only
constraint being that the customer is authorized for network access.
Another advantage of minimizing mobile node software for localized
mobility management is that multiple global mobility management
protocols can be supported. There are a variety of global mobility
management protocols that might also need support, including
proprietary or link technology-specific protocols needing support for
backward compatibility reasons. Within the Internet, both Host
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Identity Protocol (HIP) [11] and IKEv2 Mobility and Multihoming
(MOBIKE) [6] are likely to need support in addition to Mobile IPv6
[9], and Mobile IPv4 [12] support may also be necessary.
Note that this goal does NOT mean that the mobile node has no
software at all associated with mobility. The mobile node must have
some kind of global mobility protocol if it is to move from one
domain of edge mobility support to another and maintain session
continuity, although no global mobility protocol is required if the
mobile node only moves within the coverage area of the localized
mobility management protocol or no session continuity is required
during global movement. Also, if the last-hop link is a wireless
link, every wireless link protocol requires handover support on the
mobile node in the physical and medium access control layers,
typically in the wireless interface driver. Information passed from
the medium access control layer to the IP layer on the mobile node
may be necessary to trigger IP signaling for IP handover. Such
movement detection support at the IP level may be required in order
to determine whether the mobile node's default router is still
reachable after the move to a new access point has occurred at the
medium access control layer. Whether or not such support is required
depends on whether the medium access control layer can completely
hide link movement from the IP layer. For cellular type wireless
link protocols, the mobile node and network undergo an extensive
negotiation at the medium access control layer prior to handover, so
it may be possible to trigger a routing update without any IP
protocol involvement. However, for a wireless link protocol such as
IEEE 802.11 [7] in which the decision for handover is entirely in the
hands of the mobile node, IP-layer movement detection signaling from
the mobile node may be required to trigger a routing update.
The goal is that the localized mobility management solution should be
able to support any mobile node that joins the link and that has an
interface that can communicate with the network, without requiring
localized mobility management software on the mobile node.
3.8. Goal 8: Support for IPv4 and IPv6
While most of this document is written with IPv6 in mind, localized
mobility management is a problem in IPv4 networks as well. A
solution for localized mobility that works for both versions of IP is
desirable, though the actual protocol may be slightly different due
to the technical details of how each IP version works. From Goal 7
(Section 3.7), minimizing mobile node support for localized mobility
means that ideally no IP version-specific changes should be required
on the mobile node for localized mobility, and that global mobility
protocols for both IPv4 and IPv6 should be supported. Any IP
version-specific features should be confined to the network protocol.
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3.9. Goal 9: Reuse of Existing Protocols Where Sensible
Many existing protocols are available as Internet Standards upon
which the NETLMM protocol can be built. The design of the protocol
should have a goal to reuse existing protocols where it makes
architectural and engineering sense to do so. However, the design
should not attempt to reuse existing protocols where there is no real
architectural or engineering reason. For example, the suite of
Internet Standards contains several good candidate protocols for the
transport layer, so there is no real need to develop a new transport
protocol specifically for NETLMM. Reuse is clearly a good
engineering decision in this case, since backward compatibility with
existing protocol stacks is important. On the other hand, the
network-based, localized mobility management functionality being
introduced by NETLMM is a new piece of functionality, and therefore
any decision about whether to reuse an existing global mobility
management protocol should carefully consider whether reusing such a
protocol really meets the needs of the functional architecture for
network-based localized mobility management. The case for reuse is
not so clear in this case, since there is no compelling backward
compatibility argument.
3.10. Goal 10: Localized Mobility Management Independent of Global
Mobility Management
Localized mobility management should be implementable and deployable
independently of any global mobility management protocol. This
enables the choice of local and global mobility management to be made
independently of particular protocols that are implemented and
deployed to solve the two different sorts of mobility management
problems. The operator can choose a particular localized mobility
management protocol according to the specific features of their
access network. It can subsequently upgrade the localized mobility
management protocol on its own, without even informing the mobile
nodes. Similarly, the mobile nodes can use a global mobility
management protocol that best suits their requirements, or not use
one at all. Also, a mobile node can move into a new access network
without having to check that it understands the localized mobility
management protocol being used there.
The goal is that the implementation and deployment of the localized
mobility management protocol should not restrict, or be restricted
by, the choice of global mobility management protocol.
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3.11. Goal 11: Configurable Data Plane Forwarding between Local
Mobility Anchor and Mobile Access Gateway
Different network operators may require different types of forwarding
options between the LMA and the MAGs for mobile node data plane
traffic. An obvious forwarding option that has been used in past
IETF localized mobility management protocols is IP-IP encapsulation
for bidirectional tunneling. The tunnel endpoints are the LMA and
the MAGs. But other options are possible. Some network deployments
may prefer routing-based solutions. Others may require security
tunnels using IPsec Encapsulating Security Payload (ESP)
encapsulation if part of the localized mobility management domain
runs over a public access network and the network operator wants to
protect the traffic.
A goal of the NETLMM protocol is to allow the forwarding between the
LMA and MAGs to be configurable depending on the particulars of the
network deployment. Configurability is not expected to be dynamic,
as in controlled by the arrival of a mobile node; but rather,
configuration is expected to be similar in timescale to configuration
for routing. The NETLMM protocol may designate a default forwarding
mechanism. It is also possible that additional work may be required
to specify the interaction between a particular forwarding mechanism
and the NETLMM protocol, but this work is not in scope of the NETLMM
base protocol.
4. Security Considerations
There are two kinds of security issues involved in network-based
localized mobility management: security between the mobile node and
the network, and security between network elements that participate
in the NETLMM protocol. The security-related goals in this document,
described in Section 3.3 and 3.5, focus on the former, because those
are unique to network-based mobility management. The threat analysis
document [2] contains a more detailed discussion of both kinds of
threats, which the protocol design must address.
5. Acknowledgements
The authors would like to acknowledge the following people for
particularly diligent reviewing: Vijay Devarapalli, Peter McCann,
Gabriel Montenegro, Vidya Narayanan, Pekka Savola, and Fred Templin.
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6. Normative References
[1] Kempf, J., Ed., "Problem Statement for Network-Based Localized
Mobility Management (NETLMM)", RFC 4830, April 2007.
[2] Vogt, C., and Kempf, J., "Security Threats to Network-Based
Localized Mobility Management (NETLMM)", RFC 4832, April 2007.
7. Informative References
[3] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[4] Carpenter, B., "Architectural Principles of the Internet", RFC
1958, June 1996.
[5] Choi, JH. and G. Daley, "Goals of Detecting Network Attachment
in IPv6", RFC 4135, August 2005.
[6] Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)",
RFC 4555, June 2006.
[7] IEEE, "Wireless LAN Medium Access Control (MAC)and Physical
Layer (PHY) specifications", IEEE Std. 802.11, 1999.
[8] IEEE, "Port-based Access Control", IEEE LAN/MAN Standard 802.1x,
June, 2001.
[9] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
[10] Manner, J. and M. Kojo, "Mobility Related Terminology", RFC
3753, June 2004.
[11] Moskowitz, R. and P. Nikander, "Host Identity Protocol (HIP)
Architecture", RFC 4423, May 2006.
[12] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, August
2002.
[13] Soliman, H., Castelluccia, C., El Malki, K., and L. Bellier,
"Hierarchical Mobile IPv6 Mobility Management (HMIPv6)", RFC
4140, August 2005.
[14] Vida, R. and L. Costa, "Multicast Listener Discovery Version 2
(MLDv2) for IPv6", RFC 3810, June 2004.
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8. Contributors
Kent Leung
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
USA
EMail: kleung@cisco.com
Phil Roberts
Motorola Labs
Schaumberg, IL
USA
EMail: phil.roberts@motorola.com
Katsutoshi Nishida
NTT DoCoMo Inc.
3-5 Hikarino-oka, Yokosuka-shi
Kanagawa,
Japan
Phone: +81 46 840 3545
EMail: nishidak@nttdocomo.co.jp
Gerardo Giaretta
Telecom Italia Lab
via G. Reiss Romoli, 274
10148 Torino
Italy
Phone: +39 011 2286904
EMail: gerardo.giaretta@tilab.com
Marco Liebsch
NEC Network Laboratories
Kurfuersten-Anlage 36
69115 Heidelberg
Germany
Phone: +49 6221-90511-46
EMail: marco.liebsch@ccrle.nec.de
Editor's Address
James Kempf
DoCoMo USA Labs
181 Metro Drive, Suite 300
San Jose, CA 95110
USA
Phone: +1 408 451 4711
EMail: kempf@docomolabs-usa.com
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