The BGP routing information includes a community attribute domain. It is used to identify a community. The community filter specifies the matching condition for the community attribute domain.
The community attribute identifies routes with the same characteristics without considering a few IP prefixes and numerous AS numbers. Configuring community filters and community attributes simplifies route management when it is inconvenient to use IP prefix list or AS_Path filter. For example, a company branch needs to receive only routes from its headquarters and branches in adjacent countries. In this case, you can configure different community attributes for the branches. Routes in this branch can then be managed based on community attributes, without considering a few IP prefixes and numerous AS numbers of routes in different countries.
Community filters are classified into basic and advanced community filters. Compared with a basic community filter, an advanced community filter supports regular expressions and is more flexible.