Network Working Group J. Abley Internet-Draft ISC Expires: September 11, 2005 March 10, 2005 Anycast Addressing in IPv6 draft-jabley-v6-anycast-clarify-00.txt Status of this Memo This document is an Internet-Draft and is subject to all provisions of Section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 11, 2005. Copyright Notice Copyright (C) The Internet Society (2005). Abstract The IPv6 Addressing Architecture includes some restrictions on the use of anycast addresses. These restrictions were intended to protect the nascient IPv6 Internet from possible harmful consequences that might result from widespread use of anycast as a mechanism to distribute services. Since then, anycast has been widely used to distribute services using Abley Expires September 11, 2005 [Page 1] Internet-Draft Anycast Addressing in IPv6 March 2005 IPv4, and production use of anycast in IPv6 also exists. While anycast as a service distribution mechanism requires care, and is not suitable for use in all situations, many useful applications of anycast exist and the restrictions in the IPv6 Addressing Architecture are no longer appropriate. This document seeks to remove the restrictions on the use of anycast addresses from the IPv6 Addressing Architecture. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. General Applicability of Anycast . . . . . . . . . . . . . . . 3 3. Analysis of IPv6 Anycast Restrictions . . . . . . . . . . . . 3 3.1 Anycast Source Addresses . . . . . . . . . . . . . . . . . 3 3.2 Anycast Addresses on Hosts . . . . . . . . . . . . . . . . 3 4. Anycast Addresses . . . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 6. Normative References . . . . . . . . . . . . . . . . . . . . . 4 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 4 Intellectual Property and Copyright Statements . . . . . . . . 5 Abley Expires September 11, 2005 [Page 2] Internet-Draft Anycast Addressing in IPv6 March 2005 1. Introduction The IPv6 Addressing Architecture [2] includes some restrictions on the use of anycast addresses. These restrictions were intended to protect the nascient IPv6 Internet from possible harmful consequences that might result from widespread use of anycast as a mechanism to distribute services. This document seeks to remove the restrictions on the use of anycast addresses from the IPv6 Addressing Architecture. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this document are to be interpreted as described in [1]. 2. General Applicability of Anycast Anycast has seen production deployment in distributing services over both IPv4 and IPv6. However, anycast is not a suitable mechanism for all protocols, nor all routing systems. A discussion of the design considerations of an anycast service distribution strategy can be found in [3]. 3. Analysis of IPv6 Anycast Restrictions 3.1 Anycast Source Addresses For many conventional services to be distributed using anycast, it is necessary for reply datagrams sent from servers to clients to be sourced from the same address that was used as the destination in request datagrams sent from clients to servers. When such a service is distributed using anycast, the destination address used in request datagrams is necessarily an anycast address; corresponding reply packets must therefore use the same anycast address as their source address. Being able to use an anycast address as the source address in an IPv6 datagram is a prerequisite for the distribution of many services using anycast over IPv6. 3.2 Anycast Addresses on Hosts Services are provided by hosts. For a service to be distributed using anycast, datagrams directed at an anycast address must be routed to hosts so that client requests can be processed. For such datagrams to be received on hosts, it must be possible to assign anycast addresses to interfaces on those hosts. Abley Expires September 11, 2005 [Page 3] Internet-Draft Anycast Addressing in IPv6 March 2005 Being able to apply an anycast address to an interface on a host is a prerequisite for the distribution of services using anycast over IPv6. 4. Anycast Addresses Section 2.6 of RFC2373 [2] is updated as follows: o An anycast address MAY be used as the source address of an IPv6 packet. o An anycast address MAY be assigned to an IPv6 host. 5. IANA Considerations This document requests no action from IANA. 6. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 2373, July 1998. [3] Abley, J. and K. Lindqvist, "Operation of Anycast Services", Internet-Draft draft-ietf-grow-anycast-00, February 2005. Author's Address Joe Abley Internet Systems Consortium, Inc. 950 Charter Street Redwood City, CA 94063 USA Phone: +1 650 423 1317 Email: jabley@isc.org URI: http://www.isc.org/ Abley Expires September 11, 2005 [Page 4] Internet-Draft Anycast Addressing in IPv6 March 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Abley Expires September 11, 2005 [Page 5]