Re: [Idr] Why do we define so many communities for BGP
Jeffrey Haas <jhaas@pfrc.org> Tue, 08 November 2016 15:14 UTC
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Date: Tue, 08 Nov 2016 10:17:01 -0500
From: Jeffrey Haas <jhaas@pfrc.org>
To: "lizhenqiang@chinamobile.com" <lizhenqiang@chinamobile.com>
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Cc: idr <idr@ietf.org>, "draft-ietf-idr-large-community.all" <draft-ietf-idr-large-community.all@ietf.org>, "draft-ietf-idr-wide-bgp-communities.all" <draft-ietf-idr-wide-bgp-communities.all@ietf.org>, idr-chairs <idr-chairs@ietf.org>
Subject: Re: [Idr] Why do we define so many communities for BGP
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[Removing individual draft aliases.] On Tue, Nov 08, 2016 at 07:51:52PM +0800, lizhenqiang@chinamobile.com wrote: > I am confused by large community defined in draft-ietf-idr-large-community, wide community defined in draft-ietf-idr-wide-bgp-communities, extended community defined in RFC4360, community defined in RFC1997. Why do we need so many kinds of BGP communities? Can the large community be encoded in type 3 wide community? Thank you for your explaination. With specific regard to version wide communities draft -03, as part of discussion with the large communities authors on various encoding options, -03 was issued to provide suitable talking points about how various behaviors could be accomplished under a common header. As Job noted, the fundamental differences in the proposals resulted in large communities not utilizing the common header. Wide communities was not really intended to be a generic 1997 replacement and is intended to cover different goals. We will be restoring the -02 common header format so Huawei's prototype is again conformant and other prototypes will utilize that format. The Type 2 wide community which covered the 4:4 will similarly be removed since its functionality is covered by large comms. ---- With regard to the more general question, routing marking mechanisms continue to vary in format mostly to cover differing use cases. Extended communities, for example, were originally deployed primarily for BGP VPN use cases. They've proven flexible enough to cover similar abstract marking for a number of other applications, although as Job noted the 4:4 case wasn't able to fit into that format. RFC 1997 communities proved to be a good marking mechanism for generic applications over the years. For single-state marking, the well known communities fit well into that. Large communities covered the general need to expand the ability to fit AS numbers in a 1997 style marking mechanism for 4-byte ASes. As you've also noticed, those authors also added an additional field expanding the scope of 1997 communities to add the flexibility to add another "parameter". Wide communities is intended to cover more "intent-based" route marking. As a fundamental CS observation, it is understood that all marking mechanisms that have scoped namespaces can be collapsed into a smaller number of equivalence classes. This is effectively how 1997 community policy has been implemented over the years, with the mapping of functionality in those ECs present in a service provider's published community policy. However, equivalence classes make operational work more difficult since it removes more natural human and machine readable versions of the policy elements. It's this property that has encouraged a diversification in marking mechanisms. -- Jeff
- [Idr] Why do we define so many communities for BGP lizhenqiang@chinamobile.com
- Re: [Idr] Why do we define so many communities fo… Nick Hilliard
- Re: [Idr] Why do we define so many communities fo… Job Snijders
- Re: [Idr] Why do we define so many communities fo… Jeffrey Haas
- Re: [Idr] Why do we define so many communities fo… Randy Bush