BGP Large Communities

Overview

BGP routing policies control route distribution and behavior across networks. Communities, optional transitive BGP attributes associate operational metadata with routes, like origin location or specific routing actions. However, standard and extended BGP community attributes fall short in environments using 4-byte Autonomous System Numbers (ASNs).

To solve this issue, BGP introduced the Large Community (LC) attribute. It consists of an unordered set of one or more twelve-octet values, including: A 4-byte Global Administrator field (typically the ASN) and two 4-byte operator-defined fields.

These attributes enable operators to encode information pertinent to their routing policies and operational needs. Operators must not transmit duplicate values, and receiving BGP speakers must silently discard any redundant entries.

Feature Characteristics

OcNOS enhanced support for BGP Large Communities by:

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Allowing route-maps to match and manipulate multiple large-community values.

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Supporting configuration adjustments for additive operations (appending values) and deleting specific values.

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Introducing ip large-community-list to organize and reuse large-community match criteria.

For details on upgrading and downgrading versions, refer to the OcNOS Migration document.

Benefits

Scalable Policy Management: Named community-lists simplify reuse and maintenance across multiple route-maps.

Enhanced Flexibility: Additive and deletion capabilities allow policy controls without impacting other community values.

Future-Proofing: Prepares networks for advanced policy frameworks as multi-ASN and operator-specific routing needs evolve.