What communities are
A BGP community is a tag attached to a route. Standard communities look like ASN:value. Routers can match on them and change behaviour.
Informational communities
Networks tag routes with where they were learned — which city, which exchange, from a customer or a peer. This helps troubleshooting and policy.
Action communities
Many networks let customers request actions:
- Prepend when announcing to certain peers.
- Do not announce to a specific network or region.
- Lower local preference.
- Blackhole a prefix during an attack.
At an exchange
Route servers commonly support action communities that let you control which members receive your routes.
Publish your scheme
Document the communities your network sets and accepts so customers and peers can use them.
You can see communities on real routes with our looking glass.
