Policy Framework Configuration Guide - Juniper Networks

Chapter 5: Extended Match Conditions Configuration
four octets whereas the extended communities attribute is eight octets, providing a larger
range for grouping or categorizing communities. You can use community and extended
communities attributes to trigger routing decisions, such as acceptance, rejection,
preference, or redistribution.
The BGP community attribute format is as-number:community-value. The BGP extended
communities attribute format instead has three fields: type:administrator:assigned-number.
When specifying community IDs for the standard community attribute, you can use
UNIX-style regular expressions. Regular expressions are not supported for the extended
communities attribute.
NOTE: You can assign community tags to non-BGP routes through
configuration (for static, aggregate, or generated routes) or an import routing
policy. These tags can then be matched when BGP exports the routes.
To use a BGP community or extended community as a routing policy match condition,
you define the community and its members and then include the community in a match
condition.
The Junos OS supports the following standard:
• RFC 1997, BGP Communities Attribute
For configuration instructions, see the following topics:
• Defining BGP Communities and Extended Communities for Use in Routing Policy Match
Conditions on page 104
• Including BGP Communities and Extended Communities in Routing Policy Match
Conditions on page 110
• How BGP Communities and Extended Communities Are Evaluated in Routing Policy
Match Conditions on page 110
• Using Routing Policies to Prevent Advertisement of BGP Communities to Neighbors
on page 111
• Examples: Configuring BGP Communities as Routing Policy Match Conditions on
page 111
Copyright © 2010, Juniper Networks, Inc.
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