Operation Manual – IPv4 RoutingH3C S5500-EI Series Ethernet Switches Chapter 6 Routing Policy Configuration6-3V. Extended community listExtended community list (extcommunity-list) applies to BGP only. It involves twoattributes: Route-Target extcommunity for VPN, Source of Origin extcommunity. Anextcommunity-list specifies matching conditions according to the two attributes.VI. Routing policyA routing policy is used to match against some attributes in given routing informationand modify the attributes of the information if match conditions are satisfied. It canreference the above mentioned filters to define its own match criteria.A routing policy can comprise multiple nodes, which are in logic OR relationship. Eachnode is a match unit, and the system compares each node to a packet in the order ofnode sequence number. Once a node is matched, the routing policy is passed and thepacket will not go through the next node.Each node comprises a set of if-match and apply clauses. The if-match clausesdefine the match criteria. The matching objects are some attributes of routinginformation. The different if-match clauses on a node is in logical AND relationship.Only when the matching conditions specified by all the if-match clauses on the nodeare satisfied, can routing information pass the node. The apply clauses specify theactions to be performed after the node is passed, concerning the attribute settings forrouting information.6.1.3 Routing Policy ApplicationA routing policy is applied in two ways:z When redistributing routes from other routing protocols, a routing protocol acceptsonly routes passing the routing policy.z When receiving or advertising routing information, a routing protocol uses therouting policy to filter routing information.6.2 Routing Policy Configuration Task ListComplete the following tasks to configure a routing policy:TaskDefining an IPv4 prefix ListDefining an AS Path ListDefining a Community ListDefining Filtering ListsDefining an Extended Community List
