Standard communities

In a standard community, the first two bytes usually encode the AS number of the administrative entity that assigned the value in the last two bytes. In SR OS, a standard community value is configured using the format <asnum:comm-value>; the colon is a required separator character. In route policy applications, multiple standard community values can be matched with a regular expression in the format <regex1>:<regex2>, where regex1 and regex2 are two regular expressions that are evaluated one numerical digit at a time.

The following well-known standard communities are understood and acted upon accordingly by SR OS routers.

• NO_EXPORT

  When a route carries this community, it must not be advertised outside a confederation boundary (for example, to EBGP peers).

• NO_ADVERTISE

  When a route carries this community, it must not be advertised to any other BGP peer.

• NO_EXPORT_SUBCONFED

  When a route carries this community, it must not be advertised outside a member AS boundary (for example, to confed-EBGP peers or EBGP peers.

• LLGR_STALE

  When a route carries this community, it indicates that the route was propagated by a router that is a long-lived graceful restart helper and normally (in the absence of LLGR) the route would have been withdrawn.

• NO_LLGR

  When a route carries this community, it indicates that the route should not be retained and used past the normal graceful restart window of time.

• BLACKHOLE

  When a route carries this community, it indicates that the route should be installed into the FIB with a blackhole next-hop.

Standard communities can be added to or removed from BGP routes using BGP import and export policies. When a BGP route is locally originated by exporting a static or aggregate route into BGP, and the static or aggregate route has one or more standard communities, these community values are automatically added to the BGP route. This may affect the advertisement of the locally originated route if one of the well-known communities is associated with the static or aggregate route.

To remove all the standard communities from all routes advertised to a BGP peer, use the disable-communities standard command.