BGP Large Communities Attribute
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J. Heitz, J. Snijders, K. Patel, I. Bagdonas, N. Hilliard · 2017-02
Abstract
RFC 8092 defines the BGP Large Communities attribute, which carries a set of 4-octet Global Administrator fields combined with two 4-octet Local Data fields. This provides a 12-byte community value space that accommodates 4-byte ASNs without the encoding workarounds required by the original 2-byte BGP Communities attribute (RFC 1997) and Extended Communities (RFC 4360).
Why This RFC Matters
As the Internet moved to 4-byte ASNs (RFC 6793), the original 2-byte community attribute became unwieldy for encoding the originating AS alongside policy data. BGP Large Communities provide a clean, human-readable format (ASN:policy:value) that is now widely used by IXPs, route servers, and network operators for signaling routing policy across AS boundaries—replacing a maze of AS-specific community encoding conventions.