BGP communities
BGP communities provide additional capability for tagging routes and modifying BGP routing policy on upstream and downstream routers. They can be appended, removed, or modified on each attribute as the route travels from router to router.
BGP communities are an optional transitive BGP attribute that can traverse from autonomous system to autonomous system. A BGP community is a 32-bit number that can be included with a route. It can be displayed as two 16-bit numbers (0-65535):(0-65535).