BGP Attributes
BGP chooses a route to network based on the attributes of its path. Four
categories of attributes exist:
�¡ Well-known mandatory.Must be recognized by all BGP routers,
present in all BGP updates, and passed on to other BGP routers. For
example, AS path, origin, and next hop.
�¡ Well-known discretionary.Must be recognized by all BGP routers
and passed on to other BGP routers, but need not be present in an
update. For example, local preference.
�¡ Optional transitive.Might or might not be recognized by a BGP
router, but is passed on to other BGP routers. If not recognized, it is
marked as partial. For example, aggregator, community.
�¡ Optional nontransitive.Might or might not be recognized by a BGP
router and is not passed on to other routers. For example, Multi-Exit
Discriminator (MED), originator ID.
Table 6-2 lists common BGP attributes, their meanings, and their category.