BGP Community Builder

Build and decode standard, extended, and large BGP communities. Paste a community string to decode it, or build one from scratch. Click any well-known community to load it.

// Build standard community (ASN:value)

AS Number

Value (0–65535)

// Well-known standard communities (RFC 1997)

// standard communities

Standard BGP communities are 32-bit values typically expressed as ASN:value where each part is a 16-bit number (0–65535). They are used to tag routes with policy information that can be acted on by routers.

Common uses: signal no-export to upstream, control local preference, mark customer vs peer routes, influence traffic engineering.

// Build extended community (64-bit)

Type

Sub-type format

AS Number / IP

Value

// extended communities

Extended communities (RFC 4360) are 64-bit values used primarily for MPLS VPN (L3VPN/L2VPN) route targets and origins. The Route Target (RT) identifies which VRFs import a route. The Route Origin (RO) identifies where the route originated.

Format in IOS: route-target export ASN:value inside a VRF definition.

// Build large community (ASN:value1:value2 — RFC 8092)

Global ASN

Local Data 1

Local Data 2

// large communities

Large communities (RFC 8092) are 96-bit values in ASN:local1:local2 format where all three parts are 32-bit integers. They were created to solve the problem of 4-byte ASNs making standard communities too small.

Common use: 64500:1:10 where 1=action (e.g. "do not export") and 10=peer group. Each ISP defines their own schema.

// Decode community string

// what to paste

Standard: 65001:100 or decimal 4259840100 or hex 0xFFFFF101

Large: 64500:1:10

Well-known: no-export or 65535:65281