📄 rfc2002.txt
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Network Working Group C. Perkins, Editor
Request for Comments: 2002 IBM
Category: Standards Track October 1996
IP Mobility Support
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document specifies protocol enhancements that allow transparent
routing of IP datagrams to mobile nodes in the Internet. Each mobile
node is always identified by its home address, regardless of its
current point of attachment to the Internet. While situated away
from its home, a mobile node is also associated with a care-of
address, which provides information about its current point of
attachment to the Internet. The protocol provides for registering
the care-of address with a home agent. The home agent sends
datagrams destined for the mobile node through a tunnel to the care-
of address. After arriving at the end of the tunnel, each datagram
is then delivered to the mobile node.
Table of Contents
1. Introduction 3
1.1. Protocol Requirements . . . . . . . . . . . . . . . . . . 3
1.2. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 4
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 4
1.5. New Architectural Entities . . . . . . . . . . . . . . . 5
1.6. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
1.7. Protocol Overview . . . . . . . . . . . . . . . . . . . . 8
1.8. Specification Language . . . . . . . . . . . . . . . . . 11
1.9. Message Format and Protocol Extensibility . . . . . . . . 12
2. Agent Discovery 14
2.1. Agent Advertisement . . . . . . . . . . . . . . . . . . . 14
2.1.1. Mobility Agent Advertisement Extension . . . . . 16
2.1.2. Prefix-Lengths Extension . . . . . . . . . . . . 18
2.1.3. One-byte Padding Extension . . . . . . . . . . . 19
2.2. Agent Solicitation . . . . . . . . . . . . . . . . . . . 19
2.3. Foreign Agent and Home Agent Considerations . . . . . . . 19
2.3.1. Advertised Router Addresses . . . . . . . . . . . 20
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RFC 2002 IP Mobility Support October 1996
2.3.2. Sequence Numbers and Rollover Handling . . . . . 21
2.4. Mobile Node Considerations . . . . . . . . . . . . . . . 21
2.4.1. Registration Required . . . . . . . . . . . . . . 22
2.4.2. Move Detection . . . . . . . . . . . . . . . . . 22
2.4.3. Returning Home . . . . . . . . . . . . . . . . . 24
2.4.4. Sequence Numbers and Rollover Handling . . . . . 24
3. Registration 24
3.1. Registration Overview . . . . . . . . . . . . . . . . . . 25
3.2. Authentication . . . . . . . . . . . . . . . . . . . . . 26
3.3. Registration Request . . . . . . . . . . . . . . . . . . 26
3.4. Registration Reply . . . . . . . . . . . . . . . . . . . 29
3.5. Registration Extensions . . . . . . . . . . . . . . . . . 32
3.5.1. Computing Authentication Extension Values . . . . 32
3.5.2. Mobile-Home Authentication Extension . . . . . . 33
3.5.3. Mobile-Foreign Authentication Extension . . . . . 33
3.5.4. Foreign-Home Authentication Extension . . . . . . 34
3.6. Mobile Node Considerations . . . . . . . . . . . . . . . 34
3.6.1. Sending Registration Requests . . . . . . . . . . 36
3.6.2. Receiving Registration Replies . . . . . . . . . 40
3.6.3. Registration Retransmission . . . . . . . . . . . 42
3.7. Foreign Agent Considerations . . . . . . . . . . . . . . 43
3.7.1. Configuration and Registration Tables . . . . . . 44
3.7.2. Receiving Registration Requests . . . . . . . . . 44
3.7.3. Receiving Registration Replies . . . . . . . . . 47
3.8. Home Agent Considerations . . . . . . . . . . . . . . . . 49
3.8.1. Configuration and Registration Tables . . . . . . 49
3.8.2. Receiving Registration Requests . . . . . . . . . 49
3.8.3. Sending Registration Replies . . . . . . . . . . 53
4. Routing Considerations 55
4.1. Encapsulation Types . . . . . . . . . . . . . . . . . . . 56
4.2. Unicast Datagram Routing . . . . . . . . . . . . . . . . 56
4.2.1. Mobile Node Considerations . . . . . . . . . . . 56
4.2.2. Foreign Agent Considerations . . . . . . . . . . 57
4.2.3. Home Agent Considerations . . . . . . . . . . . . 58
4.3. Broadcast Datagrams . . . . . . . . . . . . . . . . . . . 59
4.4. Multicast Datagram Routing . . . . . . . . . . . . . . . 60
4.5. Mobile Routers . . . . . . . . . . . . . . . . . . . . . 61
4.6. ARP, Proxy ARP, and Gratuitous ARP . . . . . . . . . . . 62
5. Security Considerations 66
5.1. Message Authentication Codes . . . . . . . . . . . . . . 66
5.2. Areas of Security Concern in this Protocol . . . . . . . 66
5.3. Key Management . . . . . . . . . . . . . . . . . . . . . 67
5.4. Picking Good Random Numbers . . . . . . . . . . . . . . . 67
5.5. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 67
5.6. Replay Protection for Registration Requests . . . . . . . 68
5.6.1. Replay Protection using Timestamps . . . . . . . 68
5.6.2. Replay Protection using Nonces . . . . . . . . . 69
6. Acknowledgments 71
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RFC 2002 IP Mobility Support October 1996
A. Patent Issues 72
A.1. IBM Patent #5,159,592 . . . . . . . . . . . . . . . . . . 72
A.2. IBM Patent #5,148,479 . . . . . . . . . . . . . . . . . . 72
B. Link-Layer Considerations 73
C. TCP Considerations 73
C.1. TCP Timers . . . . . . . . . . . . . . . . . . . . . . . 73
C.2. TCP Congestion Management . . . . . . . . . . . . . . . . 73
D. Example Scenarios 74
D.1. Registering with a Foreign Agent Care-of Address . . . . 74
D.2. Registering with a Co-Located Care-of Address . . . . . . 75
D.3. Deregistration . . . . . . . . . . . . . . . . . . . . . 76
E. Applicability of Prefix Lengths Extension 76
Editor's Address 79
1. Introduction
IP version 4 assumes that a node's IP address uniquely identifies the
node's point of attachment to the Internet. Therefore, a node must
be located on the network indicated by its IP address in order to
receive datagrams destined to it; otherwise, datagrams destined to
the node would be undeliverable. For a node to change its point of
attachment without losing its ability to communicate, currently one
of the two following mechanisms must typically be employed:
a) the node must change its IP address whenever it changes its
point of attachment, or
b) host-specific routes must be propagated throughout much of
the Internet routing fabric.
Both of these alternatives are often unacceptable. The first makes
it impossible for a node to maintain transport and higher-layer
connections when the node changes location. The second has obvious
and severe scaling problems, especially relevant considering the
explosive growth in sales of notebook (mobile) computers.
A new, scalable, mechanism is required for accommodating node
mobility within the Internet. This document defines such a
mechanism, which enables nodes to change their point of attachment to
the Internet without changing their IP address.
1.1. Protocol Requirements
A mobile node must be able to communicate with other nodes after
changing its link-layer point of attachment to the Internet, yet
without changing its IP address.
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RFC 2002 IP Mobility Support October 1996
A mobile node must be able to communicate with other nodes that do
not implement these mobility functions. No protocol enhancements are
required in hosts or routers that are not acting as any of the new
architectural entities introduced in Section 1.5.
All messages used to update another node as to the location of a
mobile node must be authenticated in order to protect against remote
redirection attacks.
1.2. Goals
The link by which a mobile node is directly attached to the Internet
may often be a wireless link. This link may thus have a
substantially lower bandwidth and higher error rate than traditional
wired networks. Moreover, mobile nodes are likely to be battery
powered, and minimizing power consumption is important. Therefore,
the number of administrative messages sent over the link by which a
mobile node is directly attached to the Internet should be minimized,
and the size of these messages should be kept as small as is
reasonably possible.
1.3. Assumptions
The protocols defined in this document place no additional
constraints on the assignment of IP addresses. That is, a mobile
node can be assigned an IP address by the organization that owns the
machine.
This protocol assumes that mobile nodes will generally not change
their point of attachment to the Internet more frequently than once
per second.
This protocol assumes that IP unicast datagrams are routed based on
the destination address in the datagram header (and not, for example,
by source address).
1.4. Applicability
Mobile IP is intended to enable nodes to move from one IP subnet to
another. It is just as suitable for mobility across homogeneous
media as it is for mobility across heterogeneous media. That is,
Mobile IP facilitates node movement from one Ethernet segment to
another as well as it accommodates node movement from an Ethernet
segment to a wireless LAN, as long as the mobile node's IP address
remains the same after such a movement.
One can think of Mobile IP as solving the "macro" mobility management
problem. It is less well suited for more "micro" mobility management
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RFC 2002 IP Mobility Support October 1996
applications -- for example, handoff amongst wireless transceivers,
each of which covers only a very small geographic area. As long as
node movement does not occur between points of attachment on
different IP subnets, link-layer mechanisms for mobility (i.e.,
link-layer handoff) may offer faster convergence and far less
overhead than Mobile IP.
1.5. New Architectural Entities
Mobile IP introduces the following new functional entities:
Mobile Node
A host or router that changes its point of attachment from one
network or subnetwork to another. A mobile node may change its
location without changing its IP address; it may continue to
communicate with other Internet nodes at any location using its
(constant) IP address, assuming link-layer connectivity to a
point of attachment is available.
Home Agent
A router on a mobile node's home network which tunnels
datagrams for delivery to the mobile node when it is away from
home, and maintains current location information for the mobile
node.
Foreign Agent
A router on a mobile node's visited network which provides
routing services to the mobile node while registered. The
foreign agent detunnels and delivers datagrams to the mobile
node that were tunneled by the mobile node's home agent. For
datagrams sent by a mobile node, the foreign agent may serve as
a default router for registered mobile nodes.
A mobile node is given a long-term IP address on a home network.
This home address is administered in the same way as a "permanent" IP
address is provided to a stationary host. When away from its home
network, a "care-of address" is associated with the mobile node and
reflects the mobile node's current point of attachment. The mobile
node uses its home address as the source address of all IP datagrams
that it sends, except where otherwise described in this document for
datagrams sent for certain mobility management functions (e.g., as in
Section 3.6.1.1).
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RFC 2002 IP Mobility Support October 1996
1.6. Terminology
This document frequently uses the following terms:
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