122 CHAPTER 6: IP ROUTING P ROTOCOL OPERATIONthe route is permitted by a single node in the route-policy, the route passes thematching test of the route policy without attempting the test of the next node.ACLThe access control list (ACL) used by the route policy can be divided into threetypes: advanced ACL, basic ACL and interface ACL.A basic ACL is usually used for routing information filtering. When the userdefines the ACL, the user must define the range of an IP address or subnet for thedestination network segment address, or the next-hop address of the routinginformation. If an advanced ACL is used, perform the matching operation by thespecified source address range.For details of ACL configuration, refer to Chapter 7, Using QoS/ACL Commands.IP PrefixThe function of the IP Prefix is similar to that of the ACL, but it is more flexible andeasier for users to understand. When the IP Prefix is applied to routing informationfiltering, its matching objects are the destination address information and thedomain of the routing information. In addition, in the IP Prefix, you can specify thegateway options and require it to receive only the routing information distributedby some certain routers.An IP Prefix is identified by the ip-prefix name. Each IP Prefix can include multiplelist items, and each list item can specify the match range of the network prefixforms, and is identified with an index-number. The index-number designates thematching check sequence in the IP Prefix.During the matching, the router checks list items identified by thesequence-number in ascending order. Once a single list item meets the condition,it means that it has passed the ip-prefix filtering and does not enter the testing ofthe next list item.Configuring an IPRouting PolicyConfiguring a routing policy includes tasks described in the following sections:■ Defining a Route Policy■ Defining If-match Clauses for a Route-policy■ Defining Apply Clauses for a Route Policy■ Importing Routing Information Discovered by Other Routing Protocols■ Defining IP PrefixDefining a Route PolicyA route policy can include multiple nodes. Each node is a unit for the matchingoperation. The nodes are tested against the node_number.
