3Com Router 3000 Ethernet FamilyConfiguration Guide Chapter 7 IP Routing Policy Configuration3Com Corporation7-1Chapter 7 IP Routing Policy Configuration7.1 IP Routing Policy OverviewWhen a router distributes or receives routing information, it possibly needs toimplement some policies to filter the routing information, so as to receive or distributethe routing information which can meet the specified condition only. A routing protocol,e.g. RIP, maybe need to redistribute the routing information discovered by otherprotocols to enrich its routing knowledge. While redistributing the routing information, itpossibly only needs to redistribute the information meeting the conditions and set somespecial attributes to make them meet its requirement.To implement the routing policy, you need define a set of matching rules by specifyingthe characteristics of the routing information in the routing policy under implementation.You can set the rules based on such attributes as destination address and sourceaddress of the information. The matching rules can be set in advance and then used inthe routing policy to advertise, receive and redistribute routes.Five kinds of filters, namely route-policy, ACL, AS-path, community-list and IP-prefix,are provided on a router for routing protocols to redistribute. The following will introduceeach kind of filter respectively.I. route-policyrouting policy is used for matching some attributes in given routing information and theattributes of the information will be set if the conditions are satisfied.A routing policy can comprise multiple nodes. Each node is a unit for matching test, andthe nodes will be matched on the basis of their node numbers. Each node comprises aset of if-match and apply clauses. The if-match clauses define the matching rules.The matching objects are some attributes of routing information. The different if-matchclauses on the same node is in logic AND relationship. Only when the matchingrequirements specified by all the if-match clauses on a node are satisfied, can thematching test on the node be passed. The apply clause specifies the actionsperformed after the node matching test, concerning the attribute settings of the routinginformation.The different nodes of a route-policy is in logic OR relationship. The system will checkeach node of route-policy one by one. Once the test on a route-policy node is passed, itindicates the matching test of the route-policy is passed (the test on the next-node willnot proceed).
