BGP Communities
A BGP (Border Gateway Protocol) community is a mechanism used to group multiple routes together to simplify routing policies and facilitate route management.
- Tagging Mechanism: BGP communities are essentially tags or labels that can be applied to routes, allowing routers to apply certain policies to all routes with a specific community tag.
- Format: They are typically represented as a 32-bit value, often written in the format
ASN:NN(Autonomous system number (ASN): Number) with both sides be 16-bit values.- Usage:
- Policy Control: They help in implementing routing policies such as route preference, route filtering, and traffic engineering.
- Route Management: Simplify the management of routing information by allowing bulk changes to be made to routes that share the same community tag.
- DDoS Mitigation: Specific community values, like those used in BGP blackholing (e.g.,
ASN:666), can be used to signal special actions such as dropping traffic to mitigate DDoS attacks.- Propagation: Communities are transitive, meaning they can be passed along to other routers within the same AS or to other ASes, depending on the routing policies configured.
- Flexibility: Operators can define custom community values to meet their specific needs, making BGP communities a versatile tool in network management. In summary, BGP communities are a powerful and flexible tool for managing routing policies and enhancing the control over how routes are handled and propagated across networks.