INTERNET-DRAFTIPv6 Working Group R. Hinden/NokiaHinden INTERNET-DRAFT Nokia January 4, 200226, 2004 D. Thaler Expires July 2004 Microsoft IPv6 Host to Router Load Sharing <draft-ietf-ipv6-host-load-sharing-00.txt><draft-ietf-ipv6-host-load-sharing-01.txt> Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of [RFC2026].RFC2026. 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-DraftsInternet- Drafts as reference material or to cite them other than as "work in progress." To view theThe list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories, seeDirectories can be accessed at http://www.ietf.org/shadow.html. This internet draft expires on July 4, 2002. Abstract This document defines a change to IPv6 Neighbor Discovery thatCopyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Draft IPv6 hosts can useHost to load share their outgoing traffic between multiple default routers. 1. Introduction IPv6 hosts on a LAN will usually learn about default routers by receivingRouter Advertisements sent using the IPv6 Neighbor Discovery protocol [ND]. If there are multiple routers the hosts will automatically learn about them and have multiple default routers to send off link traffic.Load Sharing January 2004 Abstract The original IPv6 Neighbor Discovery protocolconceptual sending algorithm does not require any specific procedure for hosts to divide (i.e., load share) outgoing traffic between these routers. This document defines procedures thatload-sharing among equivalent IPv6 hosts can use to load share their outgoing traffic between multiple default routers. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",routers, and "OPTIONAL"suggests schemes which can be problematic in thispractice. This document areupdates the conceptual sending algorithm so that traffic to be interpreted as described in [RFC 2119]. 2. Background RFC2461 "Neighbor Discovery for IPv6" [ND] definesdifferent destinations is distributed among routers in section 6.3.6an efficient fashion. 1. Introduction In the conceptual sending algorithm for selecting default routers. This algorithm is invoked duringin [ND] and in the optional extension in [ROUTERSEL], a next hop determinationis chosen when no destination cache entry exists for an off-link destination or when communication through an existing router is failing. Normally a router would beis selected the first time traffic is sent to a specific destination.destination IP address. Subsequent traffic to the same destination would continueaddress continues to use thisthe same router unless there wasis some otherreason to change to a different router (e.g., a redirect message is received, etc.). ND further specifies that when there are multiple reachable default routers, an implementation may always return the sameor a router (e.g.,is found to be unreachable). In both the firstbase algorithm and in the list) or may cycle through the list of reachable default routers inoptional extension, sometimes a round robin manner. It does not require any specific behavior in the casehost has a choice of multiple default routers.equivalent routers for a destination. That is, all other factors are equal and a host must break a tie via some implementation-specific means. It is desirable when there is more than one defaultequivalent router that thehosts distribute their outgoing traffic among these routers. This document changes the ND behavior to require that an implementation cycle throughshares the list of defaultload among multiple routers in a random order. 3. Load Sharing The load sharing algorithm changesand provides better performance for the host's traffic. [ND] does not require any particular behavior in this respect. It specifies that an implementation may always choose the currently specified defaultsame router selection algorithm to(e.g., the first in the list) or may cycle through the list of reachable defaultrouters in a round-robin manner. Both of these suggestions are problematic. Clearly, always choosing the same router does not provide load sharing. Some problems with naive tie-breaking techniques such as round-robin and random order. This should haveare discussed in [MULTIPATH]. While the effect of distributing outgoing traffic for new destinations amongdestination cache provides some stability since the default routers. Random selection, versus round robin,determination is used to avoid synchronizationnot per-packet, cache evictions or timeouts can still result in unstable or unpredictable paths over time, lowering the hostsperformance and making it harder to diagnose problems. Round- robin selection of a default router. Bullet 1)may also result in section 6.3.6 "Default Router Selection" [ND]synchronization issues among hosts, where in the worst case the load is replaced withconcentrated on one Draft IPv6 Host to Router Load Sharing January 2004 router at a time. In the following: 1) Routers thatremainder of this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are reachable or probably reachable (i.e.,to be interpreted as described in any state other than INCOMPLETE)[RFC2119]. 2. Load Sharing When a host chooses from multiple equivalent routers, it MUST choose using some method which distributes load for different destinations among the equivalent routers. That is, a host MUST NOT always choose the same router (e.g., the first in the list). A host SHOULD be preferred over routers whose reachability is unknown or suspect (i.e.,use a hash-based scheme, such as those described in [MULTIPATH], which takes the INCOMPLETE state, ordestination IP address into account. Note that traffic for which no Neighbor Cache entry exists). An implementation SHOULD pick routers froma given destination address will use the defaultsame router list in random order while making sure it always returnsas long as the Destination Cache Entry for the destination address is not deleted. With a reachable orhash-based scheme, traffic for a probably reachablegiven destination address will use the same router when oneover time even if the Destination Cache Entry is available. 4.deleted, as long as the list of equivalent routers remains the same. 3. Acknowledgments The authorauthors of this document would like to thank Erik Nordmark, Brian Haberman, Steve Deering, Aron Silverton, and Christian Huitema for their helpful suggestions. 5.4. Security Considerations This document requiresAs mentioned in [MULTIPATH], when next-hop selection is predictable, an nodeapplication can synthesize traffic that will all hash the same, making it possible to cycle throughlaunch a denial-of-service attack against the listload sharing algorithm, and overload a particular router. A special case of default routers. There are no known security issues withthis changeis when the same (single) next-hop is always selected, such as in the algorithm allowed by [ND]. Introducing hashing can make such an attack more difficult; the more unpredictable the hash is, the harder it becomes to conduct a denial-of-service attack against any single router. Draft IPv6 Neighbor Discovery. 6.Host to Router Load Sharing January 2004 5. Normative References [ADD-ARH] Hinden, R., S. Deering, "IP Version 6 Addressing Architecture", RFC2373, July 1988. [ICMPv6] Conta, A., S. Deering, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6)", RFC2463, December 1998. [IPv6] Deering, S., R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC2460, December 1998.[ND] Narten, T., E.Nordmark, E. and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC2461,RFC 2461, December 1998. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC2119,RFC 2119, BCP0014, March 1997. 6. Informative References [MULTIPATH] Thaler, D. and C. Hopps, "Multipath Issues in Unicast and Multicast Next-Hop Selection", RFC 2991, November 2000. [ROUTERSEL] Draves, R. and D. Thaler, "Default Router Preferences and More-Specific Routes", Work in progress, draft-ietf- ipv6-router-selection-03.txt, December 2003. 7. Author's AddressAuthors' Addresses Robert Hinden Nokia 313 Fairchild Drive Mountain View, CA 94043 USPhone: +1 650 625-2004 Email: firstname.lastname@example.org@nokia.com Dave Thaler Microsoft Corporation One Microsoft Way Redmond, WA 98052 Phone: +1 425 703 8835 EMail: email@example.com 8. Revision History (This section to be removed before publication as an RFC) Changes from draft-ietf-ipv6-router-selection-02.txt: Draft IPv6 Host to Router Load Sharing January 2004 o Split load sharing back into its own document. o Made hash-based, rather than random, the rule. 9. Full Copyright Statement Copyright (C) The Internet Society (2004). All Rights Reserved. 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