Dynamic routing

BGP community

Also called community, communities, 65001:100, community-list, set community, no-export

A tag that travels with a BGP route, written AS:value, which does nothing until a policy reads it.

A router sets it on import (set community 65001:100 for "learned from a customer") and later policies match it (bgp community-list, match community) to decide what to announce where, without listing prefixes. Providers publish menus of communities their customers can send ("do not announce to peers", "prepend twice in Europe"). Well known ones: no-export, no-advertise.

See it on real machines

Learn it on real machines.