BGP - Large BGP communities

Large BGP communities use what is known as a Large Community Attribute, which is a 12 byte value divided into three fields of four bytes each. This is an extension to the more conventional 32-bit value used for BGP communities.

Similar in syntax to conventional communities, large BGP communities use the following syntax for the 12-byte community value:

AS:function:parameter

where each of the values in the field are four bytes each.

An example of a route-policy matching a large community attribute and adjusting the local preference is shown below:

route-policy set-something
  if large-community matches-any (15562:4:3) then
    set local-preference 120
  endif
end-policy

Similarly, an example of a route-policy setting a particular large community attribute can be seen below:

route-policy set-something
  set large-community (15562:45:29) additive
end-policy

https://datatracker.ietf.org/doc/html/rfc8195 https://tools.ietf.org/html/rfc8092 https://networklessons.com/bgp/bgp-communities-explained

Links to this page: