BGP community types
A BGP community is a bit of “extra information” that you can add to one of more prefixes that is advertised to BGP neighbors. This extra information can be used for things like traffic engineering or dynamic routing policies. There are 4 well-known BGP communities that you can use or you can pick a numeric value that you can use for your own policies.
Here are the 4 well known or standard BGP communities:
- Internet: advertise the prefix to all BGP neighbors.
- No-Advertise: don’t advertise the prefix to any BGP neighbors.
- No-Export: don’t advertise the prefix to any eBGP neighbors.
- Local-AS: don’t advertise the prefix outside of the sub-AS (this one is used for BGP confederations).
You can also define what are known as extended communities which are used as a mechanism for labeling information carried in BGP. These are often used in MPLS implementations.
The way in which BGP communities are propagated between BGP routers is explained further in BGP community propagation.