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BGP Attributes


BGP attributes are broadly divided into two parts:





  1. Well Known attributes
  2. Optional attributes




Well-known attributes: "MUST" be recognized by all BGP implementations
Optional attributes: May or may not be supported by the BGP implementations





Transitive attributes: BGP process has to accept the path in which it is included and should pass it on to other peers even if these attributes are not supported. Meaning if any optional attribute is not recognized by a BGP implementation, then BGP looks to check if the transitive flag is set. If the transitive flag is set then BGP implementation should accept the attribute and advertise it to its other BGP Peers.





Non-transitive attributes: If the BGP process does not recognize the attribute then it can ignore the update and not advertise the path to its peers. If the transitive flag is not set then BGP implementation can quietly ignore the attribute, it does not have to accept and advertise this attribute to its other peers.





Well known attributes are further subdivided into:





  1. Mandatory
  2. Discretionary




Optional attributes are further divided into:





  1. Transitive
  2. Non-transitive




Well-known Mandatory Attributes
ORIGIN
AS_PATH
NEXT_HOP





Well-known Discretionary Attributes
LOCAL_PREF
ATOMIC_AGGREGATOR





Optional Transitive Attribute
AGGREGATOR
COMMUNITY





Optional non-transitive Attribute
MULTI_EXIT_DISC (MED)
ORIGINATOR_ID
CLUSTER_LIST


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