788 BigIron RX Series Configuration Guide53-1001986-01Filtering26Filtering communitiesYou can filter routes received from BGP4 neighbors based on community names.A community is an optional attribute that identifies the route as a member of a user-defined classof routes. Community names are arbitrary values made of two five-digit integers joined by a colon.You determine what the name means when you create the community name as one of a route’sattributes. Each string in the community name can be a number from 0 – 65535.This format allows you to easily classify community names. For example, a common conventionused in community naming is to configure the first string as the local AS and the second string asthe unique community within that AS. Using this convention, communities 1:10, 1:20, and 1:30can be easily identified as member communities of AS 1.The BigIron RX provides the following methods for filtering on community information:• Community filters - refer to “Defining a community filter” on page 744.• Community list ACLsNOTEThe BigIron RX cannot actively support community filters and community list ACLs at the same time.Use one method or the other but do not mix methods.NOTEOnce you define a filter or ACL, the default action for communities that do not match a filter or ACLis “deny”. To change the default action to “permit”, configure the last filter or ACL entry as “permitany any”.Community filters or ACLs can be referred to by match statements in a route map.Defining a community ACLTo configure community ACL 1, enter a command such as the following.BigIron RX(config)# ip community-list 1 permit 123:2This command configures a community ACL that permits routes that contain community 123:2.NOTERefer to “Matching based on community ACL” on page 794 for information about how to use acommunity list as a match condition in a route map.Syntax: ip community-list standard [seq ] deny | permit Syntax: ip community-list extended [seq ] deny | permit | The parameter specifies the ACL name. (If you enter a number, the CLI interprets thenumber as a text string.)The standard or extended parameter specifies whether you are configuring a standard communityACL or an extended one. A standard community ACL does not support regular expressions whereasan extended one does. This is the only difference between standard and extended IP communitylists.
