AS-PATH ATTRIBUTE CATEGORIES
- Well-known, mandatory
- Well-known, discretionary
- Optional, Transitive
- Optional, Non-transitive
WELL KNOWN, MANDATORY
This attribute MUST appear in every UPDATE message. It must be supported by all BGP software implementations. If a well-known, mandatory attribute is missing from an UPDATE message, a NOTIFICATION message must be sent to the peer.
Examples:
WELL KNOWN, DISCRETIONARY
This attribute may or may not appear in an UPDATE message, but it MUST be supported by any BGP software implmentation.
Examples:
- LOCAL_PREF
- ATOMIC_AGGREGATE
OPTIONAL, TRANSITIVE
These attributes may or may not be supported in all BGP implementations. If it is sent in an UPDATE message, but not recognized by the receiver, it should be passed on to the next AS.
Examples:
- AGGREGATOR
- COMMUNITY
OPTIONAL, NON-TRANSITIVE
May or may not be supported, but if received, it is not required that the router pass it on. It may safely and quietly ignore the optional attribute.
Examples:
- MULTI_EXIT_DISC
- ORIGINATOR_ID
- Cluster List