HP 6125G HP 6125G & 6125G/XG Blade Switches Layer 3 - IP Routing Confi - Page 130

Figure 47 BGP route-refresh message format • AFI-Address family identifier. • Res-Reserved; set to 0. • SAFI-Subsequent address family identifier. BGP path attributes Path attributes classification BGP path attributes are a group of parameters encapsulated in the path attributes field of update messages. They give detailed route attributes information that can be used for route filtering and selection. Path attributes fall into the following categories: • Well-known mandatory-Must be recognized by all BGP routers and be included in every Update message. Routing information errors occur without this attribute. • Well-known discretionary-Can be recognized by all BGP routers and optionally included in every Update message as needed. • Optional transitive-Transitive attribute between ASs. A BGP router not supporting this attribute can still receive routes with this attribute and advertise them to other peers. • Optional non-transitive-If a BGP router does not support this attribute, it will not advertise routes with this attribute. The usage of each BGP path attribute is described in the following table. Table 4 Usage of BGP path attributes Name ORIGIN AS_PATH NEXT_HOP LOCAL_PREF ATOMIC_AGGREGATE AGGREGATOR COMMUNITY MULTI_EXIT_DISC (MED) ORIGINATOR_ID CLUSTER_LIST Category Well-known mandatory Well-known mandatory Well-known mandatory Well-known discretionary Well-known discretionary Optional transitive Optional transitive Optional non-transitive Optional non-transitive Optional non-transitive Usage of BGP path attributes • ORIGIN 120