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Network Working Group                                           J. AbleyRequest for Comments: 3582                                           ISCCategory: Informational                                         B. Black                                                         Layer8 Networks                                                                 V. Gill                                                         AOL Time Warner                                                             August 2003Goals for IPv6 Site-Multihoming ArchitecturesStatus 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.Abstract   This 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.  Introduction   Site-multihoming, i.e., connecting to more than one IP service   provider, is an essential component of service for many sites which   are part of the Internet.   Current IPv4 site-multihoming practices have been added on to the   CIDR architecture [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 [6].  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.Abley, et al.                Informational                      [Page 1]

RFC 3582              IPv6 Site-Multihoming Goals            August 2003   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.  Terminology   A "site" is an entity autonomously operating a network using IP, and   in particular, determining the addressing plan and routing policy for   that network.  This definition is intended to be equivalent to   "enterprise" as defined in [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.3.  Multihoming Goals3.1.  Capabilities of IPv4 Multihoming   The following capabilities of current IPv4 multihoming practices   should be supported by an IPv6 multihoming architecture.3.1.1.  Redundancy   By multihoming, a site should be able to insulate itself from certain   failure modes within one or more transit providers, as well as   failures in the network providing interconnection among one or more   transit providers.   Infrastructural commonalities below the IP layer may result in   connectivity which is apparently diverse, sharing single points of   failure.  For example, two separate DS3 circuits ordered from   different suppliers and connecting a site to independent transit   providers may share a single conduit from the street into a building;   in this case, physical disruption (sometimes referred to as   "backhoe-fade") of both circuits may be experienced due to a single   incident in the street.  The two circuits are said to "share fate".Abley, et al.                Informational                      [Page 2]

RFC 3582              IPv6 Site-Multihoming Goals            August 2003   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.3.1.2.  Load Sharing   By multihoming, a site should be able to distribute both inbound and   outbound traffic between multiple transit providers.  This goal is   for concurrent use of the multiple transit providers, not just the   usage of one provider over one interval of time and another provider   over a different interval.3.1.3.  Performance   By multihoming, a site should be able to protect itself from   performance difficulties directly between the site's transit   providers.   For example, suppose site E obtains transit from transit providers T1   and T2, and there is long-term congestion between T1 and T2.  The   multihoming architecture should allow E to ensure that in normal   operation, none of its traffic is carried over the congested   interconnection T1-T2.  The process by which this is achieved should   be a manual one.   A multihomed site should be able to distribute inbound traffic from   particular multiple transit providers according to the particular   address range within their site which is sourcing or sinking the   traffic.Abley, et al.                Informational                      [Page 3]

RFC 3582              IPv6 Site-Multihoming Goals            August 20033.1.4.  Policy   A customer may choose to multihome for a variety of policy reasons   beyond technical scope (e.g., cost, acceptable use conditions, etc.)   For example, customer C homed to ISP A may wish to shift traffic of a   certain class or application, NNTP, for example, to ISP B as matter   of policy.  A new IPv6 multihoming proposal should provide support   for site-multihoming for external policy reasons.3.1.5.  Simplicity   As any proposed multihoming solution must be deployed in real   networks with real customers, simplicity is paramount.  The current   multihoming solution is quite straightforward to deploy and maintain.   A new IPv6 multihoming solution should not be substantially more   complex to deploy and operate (for multihomed sites or for the rest   of the Internet) than current IPv4 multihoming practices.3.1.6.  Transport-Layer Survivability   Multihoming solutions should provide re-homing transparency for   transport-layer sessions; i.e., exchange of data between devices on   the multihomed site and devices elsewhere on the Internet may proceed   with no greater interruption than that associated with the transient   packet loss during the re-homing event.   New transport-layer sessions should be able to be created following a   re-homing event.   Transport-layer sessions include those involving transport-layer   protocols such as TCP, UDP and SCTP over IP.  Applications which   communicate over raw IP and other network-layer protocols may also   enjoy re-homing transparency.3.1.7.  Impact on DNS   Multi-homing solutions either should be compatible with the observed   dynamics of the current DNS system, or the solutions should   demonstrate that the modified name resolution system required to   support them is readily deployable.3.1.8.  Packet Filtering   Multihoming solutions should not preclude filtering packets with   forged or otherwise inappropriate source IP addresses at the   administrative boundary of the multihomed site, or at the   administrative boundaries of any site in the Internet.Abley, et al.                Informational                      [Page 4]

RFC 3582              IPv6 Site-Multihoming Goals            August 20033.2.  Additional Requirements3.2.1.  Scalability   Current IPV4 multihoming practices contribute to the significant   growth currently observed in the state held in the global inter-   provider routing system; this is a concern, both because of the   hardware requirements it imposes, and also because of the impact on   the stability of the routing system.  This issue is discussed in   great detail in [6].   A new IPv6 multihoming architecture should scale to accommodate   orders of magnitude more multihomed sites without imposing   unreasonable requirements on the routing system.3.2.2.  Impact on Routers   The solutions may require changes to IPv6 router implementations, but   these changes should be either minor, or in the form of logically   separate functions added to existing functions.   Such changes should not prevent normal single-homed operation, and   routers implementing these changes should be able to interoperate   fully with hosts and routers not implementing them.3.2.3.  Impact on Hosts   The solution should not destroy IPv6 connectivity for a legacy host   implementingRFC 3513 [3],RFC 2460 [4],RFC 3493 [5], 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.Abley, et al.                Informational                      [Page 5]

RFC 3582              IPv6 Site-Multihoming Goals            August 2003   The multihoming solution may allow host or application changes if   that would enhance transport-layer survivability.3.2.4.  Interaction between Hosts and the Routing System   The solution may involve interaction between a site's hosts and its   routing system; such an interaction should be simple, scalable and   securable.3.2.5.  Operations and Management   It should be possible for staff responsible for the operation of a   site to monitor and configure the site's multihoming system.3.2.6.  Cooperation between Transit Providers   A multihoming strategy may require cooperation between a site and its   transit providers, but should not require cooperation (relating   specifically to the multihomed site) directly between the transit   providers.   The impact of any inter-site cooperation that might be required to   facilitate the multihoming solution should be examined and assessed   from the point of view of operational practicality.3.2.7.  Multiple Solutions   There may be more than one approach to multihoming, provided all   approaches are orthogonal (i.e., each approach addresses a distinct   segment or category within the site multihoming problem).  Multiple   solutions will incur a greater management overhead, however, and the   adopted solutions should attempt to cover as many multihoming   scenarios and goals as possible.4.  Security Considerations   A multihomed site should not be more vulnerable to security breaches   than a traditionally IPv4-multihomed site.   Any changes to routing practices made to accommodate multihomed sites   should not cause non-multihomed sites to become more vulnerable to   security breaches.Abley, et al.                Informational                      [Page 6]

RFC 3582              IPv6 Site-Multihoming Goals            August 20035.  Intellectual Property Statement   The IETF takes no position regarding the validity or scope of any   intellectual property 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; neither does it represent that it   has made any effort to identify any such rights.  Information on the   IETF's procedures with respect to rights in standards-track and   standards-related documentation can be found inBCP-11.  Copies of   claims of rights made available for publication and any assurances of   licenses to be made available, or the result of an attempt made to   obtain a general license or permission for the use of such   proprietary rights by implementors or users of this specification can   be obtained from the IETF Secretariat.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights which may cover technology that may be required to practice   this standard.  Please address the information to the IETF Executive   Director.6.  Normative References   [1] Fuller, V., Li, T., Yu, J. and K. Varadhan, "Classless Inter-       Domain Routing (CIDR): an Address Assignment and Aggregation       Strategy",RFC 1519, September 1993.   [2] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G. and E.       Lear, "Address Allocation for Private Internets",BCP 5,RFC1918, February 1996.   [3] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)       Addressing Architecture",RFC 3513, April 2003.   [4] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)       Specification",RFC 2460, December 1998.   [5] Gilligan, R., Thomson, S., Bound, J., McCann, J. and W. Stevens,       "Basic Socket Interface Extensions for IPv6",RFC 3493, February       2003.   [6] Huston, G., "Commentary on Inter-Domain Routing in the Internet",RFC 3221, December 2001.Abley, et al.                Informational                      [Page 7]

RFC 3582              IPv6 Site-Multihoming Goals            August 20037.  Authors' Addresses   Joe Abley   Internet Software Consortium   950 Charter Street   Redwood City, CA  94063   USA   Phone: +1 650 423 1317   EMail: jabley@isc.org   Benjamin Black   Layer8 Networks   EMail: ben@layer8.net   Vijay Gill   AOL Time Warner   EMail: vijaygill9@aol.comAbley, et al.                Informational                      [Page 8]

RFC 3582              IPv6 Site-Multihoming Goals            August 20038.  Full Copyright Statement   Copyright (C) The Internet Society (2003).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assignees.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS 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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Abley, et al.                Informational                      [Page 9]