Dynamic Configuration of IPv4 Link-Local Addresses
RFC 3927
Network Working Group S. Cheshire
Request for Comments: 3927 Apple Computer
Category: Standards Track B. Aboba
Microsoft Corporation
E. Guttman
Sun Microsystems
May 2005
Dynamic Configuration of IPv4 Link-Local Addresses
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.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
To participate in wide-area IP networking, a host needs to be
configured with IP addresses for its interfaces, either manually by
the user or automatically from a source on the network such as a
Dynamic Host Configuration Protocol (DHCP) server. Unfortunately,
such address configuration information may not always be available.
It is therefore beneficial for a host to be able to depend on a
useful subset of IP networking functions even when no address
configuration is available. This document describes how a host may
automatically configure an interface with an IPv4 address within the
169.254/16 prefix that is valid for communication with other devices
connected to the same physical (or logical) link.
IPv4 Link-Local addresses are not suitable for communication with
devices not directly connected to the same physical (or logical)
link, and are only used where stable, routable addresses are not
available (such as on ad hoc or isolated networks). This document
does not recommend that IPv4 Link-Local addresses and routable
addresses be configured simultaneously on the same interface.
Cheshire, et al. Standards Track [Page 1]
RFC 3927 IPv4 Link-Local May 2005
Table of Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements. . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Applicability . . . . . . . . . . . . . . . . . . . . . 5
1.4. Application Layer Protocol Considerations . . . . . . . 6
1.5. Autoconfiguration Issues. . . . . . . . . . . . . . . . 7
1.6. Alternate Use Prohibition . . . . . . . . . . . . . . . 7
1.7. Multiple Interfaces . . . . . . . . . . . . . . . . . . 8
1.8. Communication with Routable Addresses . . . . . . . . . 8
1.9. When to configure an IPv4 Link-Local Address. . . . . . 8
2. Address Selection, Defense and Delivery . . . . . . . . . . . 9
2.1. Link-Local Address Selection. . . . . . . . . . . . . . 10
2.2. Claiming a Link-Local Address . . . . . . . . . . . . . 11
2.3. Shorter Timeouts. . . . . . . . . . . . . . . . . . . . 13
2.4. Announcing an Address . . . . . . . . . . . . . . . . . 13
2.5. Conflict Detection and Defense. . . . . . . . . . . . . 13
2.6. Address Usage and Forwarding Rules. . . . . . . . . . . 14
2.7. Link-Local Packets Are Not Forwarded. . . . . . . . . . 16
2.8. Link-Local Packets are Local. . . . . . . . . . . . . . 16
2.9. Higher-Layer Protocol Considerations. . . . . . . . . . 17
2.10. Privacy Concerns. . . . . . . . . . . . . . . . . . . . 17
2.11. Interaction between DHCPv4 and IPv4 Link-Local
State Machines. . . . . . . . . . . . . . . . . . . . . 17
3. Considerations for Multiple Interfaces. . . . . . . . . . . . 18
3.1. Scoped Addresses. . . . . . . . . . . . . . . . . . . . 18
3.2. Address Ambiguity . . . . . . . . . . . . . . . . . . . 19
3.3. Interaction with Hosts with Routable Addresses. . . . . 20
3.4. Unintentional Autoimmune Response . . . . . . . . . . . 21
4. Healing of Network Partitions . . . . . . . . . . . . . . . . 22
5. Security Considerations . . . . . . . . . . . . . . . . . . . 23
6. Application Programming Considerations. . . . . . . . . . . . 24
6.1. Address Changes, Failure and Recovery . . . . . . . . . 24
6.2. Limited Forwarding of Locators. . . . . . . . . . . . . 24
6.3. Address Ambiguity . . . . . . . . . . . . . . . . . . . 25
7. Router Considerations . . . . . . . . . . . . . . . . . . . . 25
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
9. Constants . . . . . . . . . . . . . . . . . . . . . . . . . . 26
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