Network Working Group M. Hashimoto Internet-Draft Osaka University Expires: April 7, 2005 S. Ata Osaka City University H. Kitamura NEC Corporation M. Murata Osaka University October 7, 2004 IPv6 Anycast Terminology Definition draft-doi-ipv6-anycast-func-term-02 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 April 7, 2005. Copyright Notice Copyright (C) The Internet Society (2004). Abstract Anycast is very useful, and many researches about it are made. This document defines anycast related terms to use a term in common on the researches about anycast. In this document, we focus on network- layer anycast, which is defined in IPv6 specification [ADDR-ARCH]. M. Hashimoto Expires April 7, 2005 [Page 1] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 1. Introduction In IPv6 networks, a service-oriented address can be assigned to a interface. This address is called anycast address which identifies a set of interfaces. A packet sent to an anycast address is delivered to one of the interfaces identified by that address. The interface is nearest one according to the routing protocols' measure of distance. The purpose of this document is to clear usage of terms for IPv6 anycast and to support documents about IPv6 anycast. 2. Definition Format Definitions in this document go along with following format. Term to be defined. Definition: The specific definition for the term. Discussion: A brief discussion of the term, its application, or other information that would build understanding. [See Also:] List of other terms that are relevant to the discussion of this term. This field is optional in this document. 3. Term Definitions 3.1 Basic Terms We first define some basic terms. These definitions will assist in describing the following terminology definitions. o Anycast Address (AA) Definition: An address to be used for anycast communication. Already defined in [ANYCASTING]. Discussion: This address is service-oriented address assigned to some interfaces. The interfaces to which the same anycast address is assigned provide same service. o Anycast Packet (AP) Definition: M. Hashimoto Expires April 7, 2005 [Page 2] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 A packet whose destination address field is filled with an anycast address. Discussion: Anycast Packet is used for Anycast Comunication. When there are plural Anycast Receivers, one of the Anycast Receivers is chosen and receive an Anycast Packet. o Anycast Initiator (AI) Definition: A node that sends an anycast packet and initiates an anycast communication. Discussion: Any node can become Anycast Initiator. A node who want a particular service send an Anycast Packet and become Anycast Initiator. We use the term not "Sender" but "Initiator", because an Anycast Communication is not continuously and only first one round trip makes sense. See Also: - Anycast Communication - Anycast Responder(s) - Coresponding Anycast Responder o Anycast Responder(s) (AR) Definition: A node who can respond to a anycast packet. Discussion: Anycast Responder has an interface which is assigned an Anycast Address. One of the Anycast Responders receives an Anycast Packet which an Anycast Initiator sends. See Also: - Anycast Initiator - Coresponding Anycast Responder o Coresponding Anycast Responder (CAR) Definition: A node which actually receives an anycast packet issued from anycast initiator. Discussion: When an Anycast Initiator sends an Anycast Packet, one of the nodes in Anycast Membership is selected by Anycast Member Node M. Hashimoto Expires April 7, 2005 [Page 3] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 Selection Criteria. The selected node is called Coresponding Anycast Responder. Even if we use the same Anycast Member Node Selection Criteria, Coresponding Anycast Responder can vary node according to a differences of Anycast Initiator and network condition. See Also: - Anycast Member Node Selection Criteria - Anycast Member Node - Anycast Membership 3.2 Communication Terms o Anycast Communication Definition: A communication initiated by Anycast Initiator using an Anycast Packet. Discussion: Anycast Communication is one-way communication from Anycast Initiator to Corresponding Anycast Responder. See Also: - Anycast Initiator - Coresponding Anycast Responder o Anycast Membership Definition: A set of nodes which have interfaces assigned a same anycast address. Discussion: See Also: - Anycast Member Node - Anycast Member Link o Anycast Member Node (AMN) Definition: A node which belongs to an anycast membership. Discussion: See Also: - Anycast Membership M. Hashimoto Expires April 7, 2005 [Page 4] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 - Anycast Member Link o Anycast Member Link (AML) Definition: A link to which one or more of Anycast Member Node belong. Discussion: See Also: - Anycast Membership - Anycast Member Node o Anycast Communication Path (ACP) Definition: A path where an anycast packet traverses in anycast communication. Discussion: See Also: - Anycast Communication M. Hashimoto Expires April 7, 2005 [Page 5] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 +------------------------+ | +-----+ | | | AR1 | (Anycast: AA) | | +-----+ (Unicast: UA1) | | | +----+ Anycast Communication | +-----+ | | AI |-------------------------->| AR2 | (Anycast: AA) | +----+ | +-----+ (Unicast: UA2) | | | | +-----+ | | | AR3 | (Anycast: AA) | | +-----+ (Unicast: UA3) | +------------------------+ Anycast Membership Fig. 1 Anycast Communication 3.3 Routing Terms o Anycast Routing Definition: Forwarding anycast packets to one of the interfaces which are assigned same anycast address. Discussion: o Anycast Router Definition: A router node that can forward anycast packets according to the anycast routing. Discussion: See Also: - Anycast Routing o Anycast Member Node Selection Criteria (AMNSC) Definition: A criteria of selecting a anycast responder from an anycast membership. Discussion: See Also: - Anycast Routing - Anycast Membership M. Hashimoto Expires April 7, 2005 [Page 6] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 - Anycast Member Node o Anycast Responder Candidates (ARC) Definition: Anycast member nodes which can receive an anycast packed from one anycast initiator. Discussion: See Also: - Anycast Member Node - Anycast Initiator's Scope - Anycast Member Node's Service Zone o Anycast Initiator's Scope (AIS) Definition: A zone where an anycast packed one anycast initiator sends can reach. Discussion: In other words, a zone anycast responder candidates exist. See Also: - Anycast Responder Candidates - Anycast Member Node's Service Zone o Anycast Member Node's Service Zone (AMNSZ) Definition: A zone where anycast initiators whose anycast initiator's scope include one anycast member node exsist. Discussion: See Also: - Anycast Responder Candidates - Anycast Initiator's Scope 3.4 Address Resolving Terms o Anycast Address Resolving (AAR) Definition: To resolve an anycast address to the corresponding unicast address. M. Hashimoto Expires April 7, 2005 [Page 7] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 Discussion: We consider anycast as a service discovery mechanism [AARP]. Once an anycast receiver is discovered, the anycast initiator uses the server's unicast address for continuous communication. See Also: - Anycast Communication - Peer Unicast Address o Peer Unicast Address (PUA) Definition: An unicast address resolved from anycast address by anycast address resolving. Discussion: See Also: - Anycast Address Resolving 3.5 Addressing Terms o Anycast Address Prefix (AAP) Definition: Prefix part of a anycast address. Discussion: Anycast addresses belong to the unicast address spaces [ADDR-ARCH], but, unlike unicast, assignment of anycast addresses is not determined by the node location. Henceforth, we need to consider what kind of addresses should be assigned to the anycast address. First, we categorize into two types of anycast address. The assignment of anycast address depends on whether all anycast receivers are on the same segment or on different segments. It is also true for the anycast address assignment policy. If all anycast receivers are connected to the same segment, the anycast address can be assigned with its segment's prefix. On the other hand, if anycast receivers are on different segments, the anycast address are determined arbitrarily. See Also: - Local Anycast - Global Anycast o Local Anycast (LA) Definition: M. Hashimoto Expires April 7, 2005 [Page 8] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 An anycast in case there are anycast member nodes only in a same subnet. Discussion: An anycast address here is determined based on the anycast member node's unicast address prefix. Its interface-ID is determined arbitrarily. All anycast member nodes that share the same anycast address are connected to the same segment. In unicast routing, routers forward packets by prefix routing. Therefore, in case of local anycast, anycast packets can reach the last hop router by unicast routing. When the last hop router receives the anycast packets, anycast responder is determined by the Neighbor Cache [ND] of the last hop router. See Also: - Anycast Member node - Anycast Address Prefix - Global Anycast - Anycast Routing M. Hashimoto Expires April 7, 2005 [Page 9] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 +----+ | AI | +-+--+ | +--+-----------------------+ | | | Internet | | | +---------------------+----+ | +--+-+ | R | Anycast Router +--+-+ | ---+----+---+---------+---- | | | +--+--+ +--+--+ +--+--+ | AR1 | | AR2 | | AR3 | +-----+ +-----+ +-----+ same anycast address: AA Anycast Address AA: | n bits | 128-n bits | +------------------------------------------------+----------------+ | subnet prefix (= segments' prefix) | arbitrarily | +------------------------------------------------+----------------+ Fig. 2 Local Anycast o Global Anycast (GA) Definition: An anycast in case anycast member nodes are distributed to two or more subnets. Discussion: An anycast address here is determined arbitrarily. Anycast member nodes that share the same anycast address may not be connected to the same segment. In case of global anycast, anycast packets may not reach the last hop router by unicast routing. See Also: - Anycast Member node - Anycast Address Prefix - local Anycast - Anycast Routing M. Hashimoto Expires April 7, 2005 [Page 10] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 +----+ | AI | +-+--+ | +--+-----------------------+ | | | Internet | | | +----+-----------------+---+ | | +-+--+ Anycast +--+-+ | R1 | Router | R2 | +-+--+ +--+-+ | | --+---+-- ----+---+---- | | +--+--+ +--+--+ | AR1 | Anycast | AR2 | +-----+ Member Nodes +-----+ same anycast address: AA Anycast Address AA: | 128 bits | +-----------------------------------------------------------------+ | Anycast Address | +-----------------------------------------------------------------+ Fig. 3 Global Anycast o Anycast Seed Node (ASN) Definition: An representative anycast member node in a anycast membership, which can be reached with unicast routing only. Discussion: All other nodes belonging to a same anycast membership with an anycast seed node have the same address prefix of the anycast seed node. See Also: - Anycast Address Prefix - Anycast Routing - Sprouted Anycast Address - Non-sprouted Anycast Address M. Hashimoto Expires April 7, 2005 [Page 11] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 o Sprouted Anycast Address (SAA) Definition: An anycast address which its anycast membership includes an anycast seed node. Discussion: Sprouted anycast address's prefix is determined from anycast seed node. Packets sent to this type of anycast address are reachable at least to the anycast seed node with unicast routing only. See Also: - Anycast Address Prefix - Anycast Seed Node - Non-sprouted Anycast Address M. Hashimoto Expires April 7, 2005 [Page 12] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 +----+ | AI | +-+--+ | +--+-----------------------+ | | | Internet | | | +----+-----------------+---+ | | +-+--+ Anycast +--+-+ | R1 | Router | R2 | +-+--+ +--+-+ | | --+---+-- ----+---+---- | | +--+--+ +--+--+ | AR1 | Anycast | AR2 |<--- Anycast Seed +-----+ Member Nodes +-----+ Unicast address: UA2 same anycast address: AA Anycast Address AA: | n bits | 128-n bits | +------------------------------------------------+----------------+ | subnet prefix (= prefix of UA2) | arbitrarily | +------------------------------------------------+----------------+ Fig. 4 Sprouted Anycast Address o Non-sprouted Anycast Address (NAA) Definition: An anycast address which its anycast membership includes an anycast seed node. Discussion: Anycast address prefix of a non-sprouted anycast address may not indicate existing segment in the actual network. Without anycast routing, the packet towards this address might not reach anywhere. See Also: - Anycast Address Prefix - Anycast Seed Node - Sprouted Anycast Address 4. Security Considerations M. Hashimoto Expires April 7, 2005 [Page 13] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 This draft does not include any security issues of anycast. Other security descriptions about anycast are shown in [ANALYSIS]. M. Hashimoto Expires April 7, 2005 [Page 14] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 5. References [ANYCASTING] Partridge, C., and Mendez, T., and Milliken, T., "Host Anycasting Service," RFC1546, November 1993 [ADDR-ARCH] Hinden, R., and Deering, S., "IP Version 6 Addressing Architecture," RFC3513, April 2003. [ANALYSIS] Hagino, J., and Ettikan, K., "An Analysis of IPv6 Anycast," , June 2003 "work in progress." [SUBNET] Johnson, D., and Deering, S., "Researved IPv6 Subnet Anycast Addresses," RFC2526, March 1999. [ADDR-AUTO] Thomson, S., Narten, T., "IPv6 Stateless Address Autoconfiguration," RFC2462, December 1998. [ND] Narten, T., Nordmark, E., and Simpson, W., "Neighbor Discovery for IP Version 6 (IPv6)," RFC 2461, December 1998. [AARP] ATA, S., Kitamura, H., and Murata, M., "A Protocol for Anycast Address Resolving," , June 2002. [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. M. Hashimoto Expires April 7, 2005 [Page 15] Internet-Draft IPv6 Anycast Terminology Definition October 7, 2004 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. 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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 (2004). 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. M. Hashimoto Expires April 7, 2005 [Page 16]