Configure Community-List

Configuration Condition

None

Configure a Community-List

A Community-list is used to filter community properties of routes. Usually, a route consists of two parts: prefix and routing properties. Routing properties are different for different routing protocols. The IGP protocol usually provides simple properties such as metric, but the BGP protocol provides complex properties such as community property. A Community-list is used for filtration.

Filtration on a Community-list acts on the route on which the community property is configured. That is, if the filtration result is deny, the route instead of the community property is filtered.

Two types of Community-lists are available: standard Community-list and extended Community-list. A standard Community-list filters BGP routes based on the local-AS, internet, no-advertise, no-export properties. An extended Community-list filters BGP routes with community properties based on a regular expression.

A Community-list can be used for a routing protocol with community properties. However, you need to bind the Community-list with a route map, and then apply the route map to the routing protocol.

A Community-list contains multiple entries, and the entries are in the OR relation. When a route tries to match a Community-list, it checks the entries following the sequence of configuration. Once the route matches an entry of the community list, it passes the filtration of the community list. For the use of a regular expression in configuring an extended Community-list, refer to "Configure an AS-PATH List".

Table 15-5 Configure a community-list