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Routing Registries

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A routing registry is a repository of routing policy information and provides a place where network operators can submit, maintain, and retrieve router configuration information. A registry maintains route servers (not to be confused with routers) that coordinate routes among service provider networks, as discussed shortly. Routing servers were introduced to the Internet in 1994 by the Routing Arbiter project, which was part of the NSFNET project and managed by Merit Networks. Routing Arbiter and NAP operations were made into commercial operations in 1996 and NSF launched RSng (Route Server next generation) in 1997.

An AS (autonomous system) is a group of IP networks with its own routing policy and its own interior routing protocols. Thus, an AS is a routing domain. An AS uses BGP, an exterior gateway protocol to exchange routing information with other ASs. While interior routing is usually based on metrics derived from topology, link speed, and load, exterior routing decisions are based on policy-based rules. BGP can understand policy rules, but a mechanism to publish or communicate the policies is still required. A routing registry provides this functionality by giving ASs a way to publicize their routing policies. In addition, a relatively new language called RPSL (Routing Policy Specification Language) was developed to specify routing policies.

The IRR (Internet Routing Registry) is now the primary means of coordinating routing policy on an Internet-wide basis. It contains announced routes and routing policy in a common format that network service providers access to configure their backbone routers.

The IRR consists of national and international routing registries, including the RIPE Network Coordination Centre (NCC) in Europe, ANS (Advanced Network Solutions, Inc.), internetMCI, Bell Canada (formerly CA*net), and the RADB (Routing Arbiter Database). The RADB is a component of the IRR and provides unique services: it handles registration for all customers not covered by the other registries and coordinates the routing policies of all the other registries. The Internet also consists of regional registries, which register with one of the above national or international registries.

RPSL is a language for describing routing policy constraints and registering them in the IRR. RPSL replaces a previous language called RIPE-181 that was used through most of the 1990s. RFC 2622 (Routing Policy Specification Language, June 1999) and RFC 2650 (Using RPSL in Practice, August 1999) describe RPSL in detail.

Route Servers

Route servers are an integral part of the Internet. They provide interdomain routing services among service provider routers deployed at Internet interconnection points (NAPs and MAEs), where traffic is exchanged among the different service providers on the Internet. For a discussion of this structure, see "Internet Architecture and Backbone." Also see "Peering."

Route servers gather routing information from ISP routers, process the information according to an ISP's routing policy requirements, and forward the processed routing information to the other ISP routers at the exchange point via BGP-4. Note that route servers are not involved in traffic exchange. ISP routers at the NAPs exchange traffic directly with one another. The route servers only coordinate and provide routing information.

The advantage of placing route servers at NAPs is that ISPs can exchange routes with other ISPs by peering with the route server, rather than full-mesh BGP peering among all the ISPs on the same NAP. This arrangement helps reduce the number of peering sessions each ISP router needs to process. Each ISP may specify a routing policy and the route server processes routing information based on these policies. Policies may include filtering ISPs, specifying particular paths, and specifying which ISPs may exchange routes.

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
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