Convert between AS:value and 32-bit BGP community notation, in hex, and identify well-known community values.
RFC 1997 communities are just 32-bit integers, and AS:value is a display convention over them. Because the high half is only 16 bits, a 4-byte ASN cannot own its community space and needs RFC 8092 large communities, which give three 32-bit fields instead. Communities are how transit policy is actually signalled — customer routes, blackhole requests, regional tags — and a mismatch between the notation a peer documents and the notation your platform accepts silently drops the policy.
BGP Community
A standard community is a 32-bit value split into a 16-bit AS number and a 16-bit local value, so the decimal form is AS × 65536 + value.
Well-known communities
NO_EXPORT = 0xFFFFFF01, NO_ADVERTISE = 0xFFFFFF02, NO_EXPORT_SUBCONFED = 0xFFFFFF03.
A standard community is a 32-bit value split into a 16-bit AS number and a 16-bit local value, so the decimal form is AS × 65536 + value. RFC 1997 communities are just 32-bit integers, and AS:value is a display convention over them. Because the high half is only 16 bits, a 4-byte ASN cannot own its community space and needs RFC 8092 large communities, which give three 32-bit fields instead.
Communities are how transit policy is actually signalled — customer routes, blackhole requests, regional tags — and a mismatch between the notation a peer documents and the notation your platform accepts silently drops the policy.
This calculator takes 2 inputs: Autonomous system number, Community value. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Communities are optional transitive, but many operators strip on ingress by default. Unless the neighbour explicitly documents which communities it honours and preserves, assume yours are removed and confirm with them.