Routes can be filtered in or out of a PE by the use of an IP extended community to identify them. In this situation, a route is identified by its extended community variable. It is entered as a route target in an IP extended community list and then matched in a route-map command. This route map is then applied from the PE that is defining the route to be filtered to the PE where the route filter is to be implemented by using a neighbor route-map command. When a VRF exists on the neighbor that exports the route-target being blocked, all routes from that VRF are blocked from being sent to the PE where the filter is defined.
To define the IP extended community list 20 to define route target RT 100:6 to be denied, enter the following command.
(config)# ip extcommunity-list 20 deny rt 100:6