I believe the bigger question here is: How does bgp.tools know what the specific communities shown on the page, e.g. https://bgp.tools/communities/13335 mean? I now have this question also. Some copied examples: Community Description 13335:10106 PoP: bos01 13335:10358 PoP: cwb03 13335:10712 PoP: den04 13335:10766 PoP: maa05 13335:10920 PoP: zrh02 And here's some other copied examples from AS174 Cogent https://bgp.tools/communities/174 : Community Description 174:21000 Route is learned from NA (North America) non-customer 174:21001 Route is NA internal or customer route 174:21100 Route is learned from EU (Europe) non-customer 174:21101 Route is an EU internal or customer route 174:21200 Route is learned from AP (Asia Pacific) non-customer 174:21201 Route is an AP internal or customer route 174:22009 Italy 174:22010 Netherlands 174:22011 Portugal 174:22012 United Kingdom 174:22013 United States 174:22014 Sweden As Ronan stated, I'm not aware either of a way this is communicated by BGP itself, so somehow this documentation must exist somewhere publicly - is it only known by bgp.tools when they specifically have a route peering connection with an AS and are given the community usage details? -Bruce Wainer On Thu, Jan 22, 2026 at 4:25 PM William Herrin via NANOG < nanog@lists.nanog.org> wrote:
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/ _______________________________________________ NANOG mailing list
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