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 < [email protected]> wrote: > On Thu, Jan 22, 2026 at 12:38 PM Ronan Pigott via NANOG > <[email protected]> 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 > > https://lists.nanog.org/archives/list/[email protected]/message/MKA7UTJWKSWOWBRMMMWCXUI2FCIBLK5A/ _______________________________________________ NANOG mailing list https://lists.nanog.org/archives/list/[email protected]/message/M6FPBDJO5INH43NBQ6CW4OYC3DMK42V6/
