Source Address Selection for IPv6 FUJIKAWA Kenji Internet-Draft ROOT Inc. Expires: May 19, 2008 November 2007 Source Address Selection Just by Routing Information for IPv6 draft-fujikawa-ipv6-src-addr-selection-01.txt Status of this Memo 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 becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 May 19, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document describes a problem of source address selection Rule 8. stated in RFC3484[1], and shows one solution, which is based just on the destination based address routing and does not require policy routing such as source address based routing. FUJIKAWA Expires May 19, 2008 [Page 1] Internet-Draft Source Address Selection for IPv6 July 2007 1. A Problem of at Source Address Selection Rule 8. in RFC3484 In RFC3484[1], the source address selection guidelines are shown in the case of multihoming. However, according to them, a problem occurs that a host cannot select the best path. Rule 8 in 5. Source Address Selection in RFC3484 says: Rule 8: Use longest matching prefix. If CommonPrefixLen(SA, D) > CommonPrefixLen(SB, D), then prefer SA. Similarly, if CommonPrefixLen(SB, D) > CommonPrefixLen(SA,D), then prefer SB. Here, consider a network shown in Fig. 1. +---+ |CN | +-+-+ | 2001:db8:2001::CN | +---+---+2001:db8:2000:/36 | | +---------+ ISP2 | +----+ +----+ | | +--+ISP5+--+ISP4| | +-------+ +----+ +-+--+ | | +---+---+2001:db8:1000::/36 +------++ | | | | | ISP1 +-------------------+ ISP3 | | | | |2001:db8:3000::/36 +---+---+ +---+---+ | | | | +------------+ +------------+ 2001:db8:1000::R| |2001:db8:3000::R ++-++ 2001:db8:1001::/48| R |2001:db8:3001::/48 +-+-+ | fe80::R | 2001:db8:1001:1:EN | 2001:db8:3001:1:EN +-+-+ |EN | +---+ Fig. 1 In Fig. 1, FUJIKAWA Expires May 19, 2008 [Page 2] Internet-Draft Source Address Selection for IPv6 July 2007 - Each of ISP1, ISP2, and ISP3 is assigned an address space, 2001:db8:1000::/36, 2001:db8:2000::/36, and 2001:db8:3000::/36, respectively. - Correspondent node CN belongs to ISP2, and is assigned an address 2001:db8:2001::CN. - Router R is multihomed to ISP1 and ISP3, and distributes address spaces to downstream nodes such as 2001:db8:1001::/48 and 2001:db8:3001::/48. - End node EN is assigned two addresses, 2001:db8:1001:1:EN and 2001:db8:3001:1:EN. Here, in the above IPv6 address notation, CN, R, and EN indicates 64bit Interface ID's. According to Rule 8, by means of the longest match method, 2001:db8:3001:EN is selected as the source address of a packet directed from CN to EN. Therefore, - For the purpose of avoiding the source address filtering, policy routing or etc. is required in order to direct a packet to ISP3. - The route becomes roundabout passing through ISP3. 2. A Solution Using Just the Information of the Destination Address of Packets Here, the solution of the above problem is shown, which is based on the ordinal destination address based routing, that is, does not require policy routing such as source address based routing. This solution requires management and implementation elaborations. FUJIKAWA Expires May 19, 2008 [Page 3] Internet-Draft Source Address Selection for IPv6 July 2007 2.1 Management Elaboration +---+ |CN | +-+-+ | 2001:db8:2001::CN | +---+---+2001:db8:2000:/36 | | +---------+ ISP2 | | | | | +-------+ | +---+---+2001:db8:1000:/36 +-------+2001:db8:3000::/36 | | | | | ISP1 +-------------------+ ISP3 | | | | | +---+---+ +---+---+ | | | | +------------+ +------------+ 2001:db8:1000:R| |2001:db8:3000:R ++-++ 2001:db8:1001::/48| R |2001:db8:3001::/48 +-+-+ 2001:db8:1001:1:R | 2001:db8:3001:1:R <- A change from Fig. 1 | 2001:db8:1001:1:EN | 2001:db8:3001:1:EN +-+-+ |EN | +---+ Routing Tables: R: Destination Next Hop 2001:db8:1000::/36 address_of_ISP1's_router 2001:db8:2000::/36 address_of_ISP1's_router 2001:db8:3000::/36 address_of_ISP3's_router EN: Destination Next Hop 2001:db8:1000::/36 2001:db8:1001:1:R 2001:db8:2000::/36 2001:db8:1001:1:R 2001:db8:3000::/36 2001:db8:3001:1:R Fig.2 FUJIKAWA Expires May 19, 2008 [Page 4] Internet-Draft Source Address Selection for IPv6 July 2007 First, mange a network shown in Fig. 2. Here: - The downstream interface of router R is assigned both addresses 2001:db8:1001:R and 2001:db8:3001:R. This is required even if R has only a single downstream link. - Each of R and EN keeps the routing table shown in Fig. 2, respectively. The next hop becomes different according to a destination address, even when a single upstream router exists. 2.2 Implementation Elaboration When an entry of a routing table is hit, a source address is selected which longest-matches the next hop in the entry. In the above example, on end node EN, when the entry "2001:2::/32 2001:db8:1001:1:R" is hit for the destination "2001:db8:2001::CN", the next hop becomes "2001:db8:1001::R", as a result, the address "2001:db8:1001:1:EN" is selected, because it longest-matches the next hop. 2.3 Summary of This Method This method is summarized as follows: - When a router multihomes and is assigned multiple address spaces, it assigns multiple addresses to downstream interfaces. This is required when it has only a sigle downstream interface. - An end host has a routing table in which the next hops differs from each other when the selected route may becomes different, even when the next hop routers are the same. - An implementation is required that when an entry in a routing table is hit, a source address is selected from the interface addresses, which longest-matches the next hop. Note that the method of distributing routing information that configures the routing tables mentioned in this document, is out of the scope of this document. Some intra-domain routing protocol may be adaptable. FUJIKAWA Expires May 19, 2008 [Page 5] Internet-Draft Source Address Selection for IPv6 July 2007 Author's Address FUJIKAWA Kenji ROOT Inc., Kyoto Information Laboratory 59 Minami-yonnotsubo-cho, Iwakura, Sakyo-ku, Kyoto 606-0033, Japan Phone: +81-3-5436-8380 (Ext. 1593) Email: fujikawa@root-hq.com References [1] R. Draves, "Default Address Selection for Internet Protocol version 6 (IPv6)", RFC3484, Feburary 2003. FUJIKAWA Expires May 19, 2008 [Page 6] Internet-Draft Source Address Selection for IPv6 July 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). 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. 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, THE IETF TRUST 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. 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