Re: What's up with BGP communities?

[William Herrin via NANOG <nanog () lists nanog org>]

On Thu, Jan 22, 2026 at 1:55 PM Ronan Pigott <ronan () rjp ie> wrote:
> IIUC, a "route map" is a configuration local to the BGP router. So, an
> operator may make some decision about the meaning of a community and then
> attach it to routes advertised to their peers, but no peer can reasonably
> act on the community information without understanding the meaning intended
> by the owner, right?

Correct.

> So if I operated a network and my BGP peer advertises
> routes that belong to a bunch of communities, how can I possibly learn the
> intended meaning of those communities to configure a sensible route map for
> my router?

You ask your peer. In some cases, the peer writes a web page which
explains what their communities mean so that they can just say, "look
at this web page." And then you have sites like bgp.tools which
collect the information from the various web pages individual networks
have published into a large database.

Because the communities have arbitrary meanings, those meanings are
communicated person to person, not machine to machine.

Regards,
Bill Herrin


-- 
For hire. https://bill.herrin.us/resume/
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