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