BGP Communities

BGP communities are 32-bit values which are attached to a BGP route in order to carry additional information about that route. In common usage, this 32-bit value is split into two 16-bit values seperated by a colon (:), where the first half typically represents the ASN that the community "belongs to", and the second half typically represents the arbitrary data.

Informational Communities

Informational Communities are BGP communities added by nLayer, in order to convey information about how and where the route was initially learned by our network. These communities will always have 5 digits in the second half, and are constructed in the following format:

4436:TCRPP

T The type of relationship that the route was learned through.
C The continent where the route was learned.
R The region of the continent where the route was learned.
PP The POP code (cityde) where the route was learned. 

Export Action Communities

Export Action Communities are optional values which may be added by nLayer customers to how routes are exported to other networks. These communities may also be targetted to specific neighbor ASNs, specific locations (continents, regions, or cities), or specific classes of neighbors (transits, peers, customers). Export Action Communities are always 4 digits in length in the second half, and have the following structure:

#####:A0CR
-or-
#####:A1PP
 

##### The target ASN
A The action code to be performed
C The target continent (same table as above)
R The target region (same table as above)
PP The target POP (city code, same table as above)

Local Preference Communities

Local Preference Communities are values which influence the best-path selection of BGP prefixes. The local-preference attribute is not transitive, so this applies only to path selection within the nLayer network. A value of 50 will create a "backup route" that is never used or propagated to the rest of the Internet, so long as any other path is heard for the prefix in question. 

Other Communities

These are miscellaneous communities which do not fit into any of the formats above. The Multihomed Customer Advisory Tag is used to automatically indicate any known issues, such as congestion or routing problems, so that multihomed customers can match this community and divert traffic to another path, if possible.