On Thu, Jan 22, 2026 at 12:38 PM Ronan Pigott via NANOG <nanog@lists.nanog.org> wrote:
I want to know, where does this supplementary information about the communities come from, in this case the "PoP: blah" bits? I don't think it is communicated by BGP directly, so is there some standard out of band mechanism to describe the communities? Or am I just ignorant of this BGP feature?
Hi Ronan, A BGP community is an arbitrary label attached to a route. It means whatever the person who wrote the label wants it to mean. A BGP router has "route maps" which can use or set these "labels" on routes that it has received. For example, a route map may say, "If community X then make this route a lower priority than others." Or it might say, "If community Y, discard and don't use this route." Route maps can also set communities. For example, they can say: "If the route came from this place, set community X." Then someone else on a different router can say, "If community X then I know the route came from that place and I want to do something non-default with it, such as discarding it." Like so many things in routing, the use of the terminology "community" is weird and confusing. It's just an arbitrary label that means whatever the person who defined it wants it to mean. Make sense? Regards, Bill Herrin -- For hire. https://bill.herrin.us/resume/