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    Creating an IP Extended Community List for BGP

    You can use the ip extcommunity-list command to create an extended community list for BGP and control access to it. A route can belong to any number of communities, so an extended community list can have many entries comprising many communities.

    You can specify one or more community values when you create an extended community list. A clause in a route map that includes a list that has more than one value matches only a route that has all the values; that is, the multiple values are logically joined by an AND operator.

    You can use the rt keyword to specify a route target community, which consists of one or more routers that can receive a set of routes advertised by BGP that carry the extended community attribute.

    You can use the soo keyword to specify a site-of-origin community, which consists of one or more routers that inject into BGP a set of routes that carry the extended community attribute.

    To create an extended community list for BGP and assign the created extended community list to a route map:

    • Create an extended community list.
      host1(config)#ip extcommunity-list boston1 permit rt 100:2 rt 100:3 rt 100:4
    • Match the created extended community list to a route map. A route matches this community list only if it belongs to at least all three communities in the extended community list boston1: communities 100:2, 100:3, and 100:4.
      host1(config)#route-map marengo permit 10 host1(config-route-map)#match extcommunity boston1

    Use the no ip extcommunity-list command to remove a single extended community list entry if you specify the permit or deny keyword and a path expression. Otherwise, the router removes the entire community list.

    Published: 2014-08-12