Google Network Working Group J. Please refer to the current edition of the "Internet Official Protocol Standards" STD 1 for the standardization state and status of this protocol. Distribution of this memo is unlimited. All Rights Reserved. When used with UDP, responses to requests are returned to the source address the request came from, and to the port written into the topmost Via header field value of the request. This behavior is not desirable in many cases, most notably, when the client is behind a Network Address Translator NAT.
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Black Layer8 Networks V. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. 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. Introduction Site-multihoming, i. Current IPv4 site-multihoming practices have been added on to the CIDR architecture , 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. 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 . A "transit provider" operates a site that directly provides connectivity to the Internet to one or more external sites. A "multihomed" site is one with more than one transit provider. Multihoming Goals 3. Capabilities of IPv4 Multihoming The following capabilities of current IPv4 multihoming practices should be supported by an IPv6 multihoming architecture.
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". 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.
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.
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.
Policy A customer may choose to multihome for a variety of policy reasons beyond technical scope e. A new IPv6 multihoming proposal should provide support for site-multihoming for external policy reasons. 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. Transport-Layer Survivability Multihoming solutions should provide re-homing transparency for transport-layer sessions; i.
New transport-layer sessions should be able to be created following a re-homing event. Applications which communicate over raw IP and other network-layer protocols may also enjoy re-homing transparency.
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. 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.
Additional Requirements 3. 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 . A new IPv6 multihoming architecture should scale to accommodate orders of magnitude more multihomed sites without imposing unreasonable requirements on the routing system. 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.
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. The multihoming solution may allow host or application changes if that would enhance transport-layer survivability.
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. Multiple Solutions There may be more than one approach to multihoming, provided all approaches are orthogonal i.
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. 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.
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RFC 3582 - Goals for IPv6 Site-Multihoming Architectures
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