A Framework for Inter-Domain Route Aggregation
RFC 2519
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Document |
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RFC - Informational
(February 1999; No errata)
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Authors |
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Enke Chen
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John Stewart
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Last updated |
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2013-03-02
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IETF
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plain text
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(None)
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Document shepherd |
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No shepherd assigned
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IESG |
IESG state |
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RFC 2519 (Informational)
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Consensus Boilerplate |
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Unknown
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Network Working Group E. Chen
Request for Comments: 2519 Cisco
Category: Informational J. Stewart
Juniper
February 1999
A Framework for Inter-Domain Route Aggregation
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 (1999). All Rights Reserved.
Abstract
This document presents a framework for inter-domain route aggregation
and shows an example router configuration which 'implements' this
framework. This framework is flexible and scales well as it
emphasizes the philosophy of aggregation by the source, both within
routing domains as well as towards upstream providers, and it also
strongly encourages the use of the 'no-export' BGP community to
balance the provider-subscriber need for more granular routing
information with the Internet's need for scalable inter-domain
routing.
1. Introduction
The need for route aggregation has long been recognized. Route
aggregation is good as it reduces the size, and slows the growth, of
the Internet routing table. Thus, the amount of resources (e.g., CPU
and memory) required to process routing information is reduced and
route calculation is sped up. Another benefit of route aggregation
is that route flaps are limited in number, frequency and scope, which
saves resources and makes the global Internet routing system more
stable.
Since CIDR (Classless Inter-Domain Routing) [2] was introduced,
significant progress has been made on route aggregation, particularly
in the following two areas:
- Formulation and implementation of IP address allocation policies
by the top registries that conform to the CIDR principles [1].
Chen & Stewart Informational [Page 1]
RFC 2519 Inter-Domain Route Aggregation February 1999
This policy work is the cornerstone which makes efficient route
aggregation technically possible.
- Route aggregation by large (especially "Tier 1") providers. To
date, the largest reductions in the size of the routing table
have resulted from efficient aggregation by large providers.
However, the ability of various levels of the global routing system
to implement efficient aggregation schemes varies widely. As a
result, the size and growth rate of the Internet routing table, as
well as the associated route computation required, remain major
issues today. To support Internet growth, it is important to
maximize the efficiency of aggregation at all levels in the routing
system.
Because of the current size of the routing system and its dynamic
nature, the first step towards this goal is to establish a clearly
defined framework in which scaleable inter-domain route aggregation
can be realized. The framework described in this document is based
on the predominant and current experience in the Internet. It
emphasizes the philosophy of aggregation by the source, both within
routing domains as well as towards upstream providers. The framework
also strongly encourages the use of the "no-export" BGP community to
balance the providersubscriber need for more granular routing
information with the Internet's need for scalable inter-domain
routing. The advantages of this framework include the following:
- Route aggregation is done in a distributed fashion, with
emphasis on aggregation by the party or parties injecting the
aggregatable routing information into the global mesh.
- The flexibility of a routing domain to be able to inject more
granular routing information to an adjacent domain to control
the resulting traffic patterns, without having an impact on the
global routing system.
In addition to describing the philosophy, we illustrate it by
presenting sample configurations. IPv4 prefixes, BGP4 and ASs
are used in examples, though the principles are applicable to
inter-domain route aggregation in general.
Address allocation policies and technologies to renumber entire
networks, while very relevant to the realization of successful
and sustained inter-domain routing, are not the focus of this
document. The references section contains pointers to relevant
documents [8, 9, 11, 12].
Chen & Stewart Informational [Page 2]
RFC 2519 Inter-Domain Route Aggregation February 1999
2. Route Aggregation Framework
The framework of inter-domain route aggregation we are proposing can
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