BGP Community Builder
Communities are tags carried with a route. They mean whatever the network carrying them has decided they mean — with a handful of exceptions that are standardised.
Local toolYour network plan stays in your browser. Nothing you enter is uploaded, logged, or sent to any server.
Standard, large, and what they actually mean
A standard community is 32 bits, written as two 16-bit halves —
65000:100. Convention puts the ASN first and a value the ASN chose second.
A large community is 96 bits in three 32-bit parts —
65000:1:200. It exists because 32-bit ASNs do not fit in a 16-bit half, which made
standard communities unusable for a growing share of the internet.
Most values mean nothing universally. 65000:100 means whatever
AS 65000 published that it means, usually in a document on their website. Do not assume a
community you have seen elsewhere carries the same meaning here.
A few are standardised. no-export (65535:65281) asks that the
route not be advertised outside the receiving AS; no-advertise (65535:65282) asks
that it not be advertised to any peer at all. These are honoured broadly, though honouring them
is still a policy decision at each network.
Communities are how customers signal intent to a provider — prepend here, do not export there, set a local preference. What each provider accepts is entirely up to them.
Related tools
AS-Path Visualizer and the Best-Path Simulator cover the attributes that decide routing.