BGP – Path Attributes

Attribributes combined together make up the “metric” or believability of a BGP route.

Well-Known, Mandatory

These attributes must be supported for RFC compliance.

  • AS-Path
  • Next-hope
  • Origin

Well-Known, Discretionary

Industry standard and documented under RFC. They do not need to be included in a routing announcement but can be.

  • Local Preference
  • Atomic Aggregate

Optional, Transistive

Optional means that the attribute does not have to be supported in a BGP implementation – i.e. out of RFC spec. Transititive means the attibute will be passed on however.

  • Aggregator
  • Community

Optional, Not-Transisitive

Optional means that the attribute does not have to be supported in a BGP implementation – i.e. out of RFC spec. Non-Transititive means the attibute doesn’t need to be passed on.

  • MED (Metric)
  • Originator ID
  • Cluster

Notes:

AS-PATH attribute can be used for loop prevention.

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