Network Working Group J. Abley Request for Comments: 3582 ISC Category: Informational B. Black Layer8 Networks V. Gill AOL Time Warner August 2003 Goals for IPv6 Site-Multihoming Architectures Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved.
AbstractThis document outlines a set of goals for proposed new IPv6 site- multihoming architectures. It is recognised that this set of goals is ambitious and that some goals may conflict with others. The solution or solutions adopted may only be able to satisfy some of the goals presented here. 1], which assumes that routing table entries can be aggregated based upon a hierarchy of customers and service providers. However, it appears that this hierarchy is being supplanted by a dense mesh of interconnections . Additionally, there has been an enormous growth in the number of multihomed sites. For purposes of redundancy and load-sharing, the multihomed address blocks are introduced into the global table even if they are covered by a provider aggregate. This contributes to the rapidly-increasing size of both the global routing table and the turbulence exhibited within it, and places stress on the inter-provider routing system.
Continued growth of both the Internet and the practice of site- multihoming will seriously exacerbate this stress. The site- multihoming architecture for IPv6 should allow the routing system to scale more pleasantly. 2]. A "transit provider" operates a site that directly provides connectivity to the Internet to one or more external sites. The connectivity provided extends beyond the transit provider's own site. A transit provider's site is directly connected to the sites for which it provides transit. A "multihomed" site is one with more than one transit provider. "Site-multihoming" is the practice of arranging a site to be multihomed. The term "re-homing" denotes a transition of a site between two states of connectedness due to a change in the connectivity between the site and its transit providers' sites.
The multihoming architecture should accommodate (in the general case, issues of shared fate notwithstanding) continuity of connectivity during the following failures: o Physical failure, such as a fiber cut, or router failure, o Logical link failure, such as a misbehaving router interface, o Routing protocol failure, such as a BGP peer reset, o Transit provider failure, such as a backbone-wide IGP failure, and o Exchange failure, such as a BGP reset on an inter-provider peering.
6]. A new IPv6 multihoming architecture should scale to accommodate orders of magnitude more multihomed sites without imposing unreasonable requirements on the routing system. RFC 3513 , RFC 2460 , RFC 3493 , and other basic IPv6 specifications current in April 2003. That is to say, if a host can work in a single-homed site, it should still be able to work in a multihomed site, even if it cannot benefit from site- multihoming. It would be compatible with this goal for such a host to lose connectivity if a site lost connectivity to one transit provider, despite the fact that other transit provider connections were still operational. If the solution requires changes to the host stack, these changes should be either minor, or in the form of logically separate functions added to existing functions. If the solution requires changes to the socket API and/or the transport layer, it should be possible to retain the original socket API and transport protocols in parallel, even if they cannot benefit from multihoming.
The multihoming solution may allow host or application changes if that would enhance transport-layer survivability.
 Fuller, V., Li, T., Yu, J. and K. Varadhan, "Classless Inter- Domain Routing (CIDR): an Address Assignment and Aggregation Strategy", RFC 1519, September 1993.  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G. and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996.  Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6) Addressing Architecture", RFC 3513, April 2003.  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998.  Gilligan, R., Thomson, S., Bound, J., McCann, J. and W. Stevens, "Basic Socket Interface Extensions for IPv6", RFC 3493, February 2003.  Huston, G., "Commentary on Inter-Domain Routing in the Internet", RFC 3221, December 2001.
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