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Configuring BGP Working with Communities
OmniSwitch 6800/6850/9000 Advanced Routing Configuration Guide December 2007 page 4-43
Working with Communities
Distribution of routing information in BGP is typically based on IP address prefixes or on the value of the
AS_PATH attributes. To facilitate and simplify the control of routing information, destinations can be
grouped into communities and routing decisions can be applied based on these communities.
Communities are identified by using the numbering convention of the AS and the community number,
separated by a colon (for example, 200:500)
There are a few well known communities defined (in RFC 1997) that do not require the numbering
convention. Their community numbers are reserved and thus can be identified by name only. These are
listed below:
• no-export. Routes in this community are advertised within the AS but not beyond the local AS.
• no-advertise. Routes in this community are not advertised to any peer.
• no-export-subconfed. Routes in this community are not advertised to any external BGP peer.
Communities are added to routes using the policy commands, as described in “Routing Policies” on
page 4-45.