Network Working Group B. Black Internet-Draft Layer8 Networks Expires: December 24, 2001 V. Gill J. Abley Metromedia Fiber Network Inc. June 25, 2001 Requirements for IP Multihoming Architectures draft-ietf-multi6-multihoming-requirements-01 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of 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-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 December 24, 2001. Copyright Notice Copyright (C) The Internet Society (2001). All Rights Reserved. Abstract Multihoming is an essential component of service for enterprises [3] which are part of the Internet. Existing IPv4 multi-homing practices, described in a companion draft [1], provides a set of capabilities that must be accommodated by the adopted multi-homing architecture in IPv6, and a set of limitations that must be overcome, relating in particular to scalability. This document outlines a set of requirements for a new IPv6 multi- homing architecture. Black, et. al. Expires December 24, 2001 [Page 1] Internet-Draft IP Multihoming Requirements June 2001 1. Introduction Multihoming is an essential component of service for enterprises which are part of the Internet. Current IPv4 multihoming practices have been added on to the CIDR architecture [2], which assumes that routing table entries can be aggregated based upon a hierarchy of customers and service providers [1]. However, it appears that this hierarchy is being supplanted by a dense mesh of interconnections [9]. Additionally, there has been an enormous growth in the number of multihomed organizations. For purposes of redundancy and load sharing, the multihomed customer blocks, which are almost always a longer prefix from the provider aggregate, are announced, along with the larger aggregate by the provider. This results in rapidly increasing size of the global routing table. This explosion places significant stress on the inter-provider routing system. Migration to IPv6, which will allow unprecedented scaling of the number of potentially multihomed sites, will seriously exacerbate this stress unless a substantially different approach to multihoming is adopted. Black, et. al. Expires December 24, 2001 [Page 2] Internet-Draft IP Multihoming Requirements June 2001 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [4]. An "enterprise" is an entity autonomously operating a network using TCP/IP and, in particular, determining the addressing plan and address assignments within that network. This is the definition of "enterprise" used in [3]. A "transit provider" is an enterprise which provides connectivity to the Internet to one or more other enterprises. The connectivity provided extends beyond the transit provider's own network. A "multi-homed" enterprise is one with more than one transit provider. "Multihoming" is the practice of being multi-homed. The term "re-homing" denotes a transition of an enterprise between two states of connectedness, due to a change in the connectivity between the enterprise and its transit providers. Black, et. al. Expires December 24, 2001 [Page 3] Internet-Draft IP Multihoming Requirements June 2001 3. Multihoming Requirements 3.1 Capabilities of IPv4 Multihoming The following capabilities of current IPv4 multihoming practices are required to be supported by an IPv6 multihoming architecture. IPv4 multihoming is discussed in more detail in [1]. 3.1.1 Redundancy By multihoming, an enterprise should be able to insulate itself from certain failure modes within one or more transit providers, as well as failures in the network providing interconnecting with one or more transit providers. The multihoming architecture must accommodate (in the general case, issues of shared-fate notwithstanding) the following failure modes: o Physical link 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, an enterprise should be able to distribute both inbound and outbound traffic between multiple transit providers. 3.1.3 Performance By multihoming, an enterprise should be able to protect itself from performance difficulties between transit providers. For example, suppose enterprise 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. A multi-homed enterprise must also be able to distribute inbound traffic particular multiple transit providers according to the Black, et. al. Expires December 24, 2001 [Page 4] Internet-Draft IP Multihoming Requirements June 2001 particular network within their enterprise which is sourcing or sinking the traffic. 3.1.4 Policy A customer may choose to multihome for a variety of policy reasons outside 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 must provide support for 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 proposal must not be substantially more complex to deploy and operate than current IPv4 multihoming practices. 3.1.6 Transport-Layer Survivability Multihoming solutions must provide re-homing transparency for transport-layer protocols; i.e. exchange of data between devices on the multi-homed enterprise network 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 must also be able to be created following a re-homing event. 3.2 Additional Requirements 3.2.1 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 [9]. A new IPv6 multihoming architecture should scale to accommodate orders of magnitude more multi-homed enterprises without imposing unreasonable requirements on the routing system. Black, et. al. Expires December 24, 2001 [Page 5] Internet-Draft IP Multihoming Requirements June 2001 3.2.2 Impact on Routers The solution may require changes to IPv6 router implementations, but these changes must be either minor, or in the form of logically separate functions added to existing functions. Such changes must not prevent normal single-homed operation, and routers implementing these changes must be able to interoperate fully with hosts and routers not implementing them. 3.2.3 Impact on Hosts The solution must not destroy IPv6 connectivity for a legacy host implementing RFC 2373 [5], RFC 2460 [7], RFC 2553 [8] and other basic IPv6 specifications current in June 2001. That is to say, if a host can work in a single-homed site, it must still be able to work in a multihomed site, even if it cannot benefit from multihoming. It would be compatible with this requirement for such a host to lose connectivity if the site's primary ISP connection failed. If the solution requires changes to the host stack, these changes must 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 must be possible to retain the original socket API and transport protocols in parallel, even if they cannot benefit from multihoming. The multi-homing solution should allow host or application changes to enhance session 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; this interaction should be simple, scaleable and securable. 3.2.5 Operations and Management It must be posssible to monitor and configure the multihoming system. Black, et. al. Expires December 24, 2001 [Page 6] Internet-Draft IP Multihoming Requirements June 2001 4. Security Considerations Multihoming no doubt offers some attractive opportunites for denial of service and spoofing attacks. Multihomed sites must be protected against such attacks at least as well as single-homed sites. Black, et. al. Expires December 24, 2001 [Page 7] Internet-Draft IP Multihoming Requirements June 2001 References [1] Abley, J., Black, B. and V. Gill, "IPv4 Multihoming Motivation, Practices and Limitations (work-in-progress)", I-D draft-ietf- multi6-v4-multihoming-00, June 2001, . [2] Fuller, V., Li, T., Yu, J. and K. Varadhan, "Classless Inter- Domain Routing (CIDR): an Address Assignment and Aggregation Strategy", RFC 1519, September 1993. [3] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G. and E. Lear, "Address Allocation for Private Internets", RFC 1918, February 1996. [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [5] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 2373, July 1998. [6] Hinden, R., O'Dell, M. and S. Deering, "An IPv6 Aggregatable Global Unicast Address Format", RFC 2374, July 1998. [7] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [8] Gilligan, R., Thomson, S., Bound, J. and W. Stevens, "Basic Socket Interface Extensions for IPv6", RFC 2553, March 1999. [9] Huston, G., "Analyzing the Internet's BGP Routing Table", January 2001. Authors' Addresses Benjamin Black Layer8 Networks EMail: ben@layer8.net Black, et. al. Expires December 24, 2001 [Page 8] Internet-Draft IP Multihoming Requirements June 2001 Vijay Gill Metromedia Fiber Network Inc. 8075 Leesburg Pike Suite 300 Vienna, VA 22182 US Phone: +1 410 262 0660 EMail: vgill@mfnx.net Joe Abley Metromedia Fiber Network Inc. 2204 Pembroke Court Burlington, ON L7P 3X8 Canada Phone: +1 905 319 9064 EMail: jabley@mfnx.net Black, et. al. Expires December 24, 2001 [Page 9] Internet-Draft IP Multihoming Requirements June 2001 Full Copyright Statement Copyright (C) The Internet Society (2001). All Rights Reserved. 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