Overview of BGP Communities and Extended Communities as Routing Policy Match Conditions
A BGP community is a group of destinations that share a common property. Community information is included as a path attribute in BGP update messages. This information identifies community members and allows you to perform actions on a group without having to elaborate upon each member. You can create a named community and include it in a routing policy with the community match condition, which is described in Configuring Match Conditions in Routing Policy Terms. For a list of the actions that can be configured for communities, see Configuring Actions That Manipulate Route Characteristics.
You can configure the standard community attribute and the extended communities attribute for inclusion in BGP update messages. The standard community attribute is 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
- Including BGP Communities and Extended Communities in Routing Policy Match Conditions
- How BGP Communities and Extended Communities Are Evaluated in Routing Policy Match Conditions
- Using Routing Policies to Prevent Advertisement of BGP Communities to Neighbors
- Examples: Configuring BGP Communities as Routing Policy Match Conditions
