3com 5500-SI Manual De Usuario

IP Routing Policy 259

and the matching objects are attributes of routing information. The relationship of 

clauses for a node uses a series of Boolean “AND” statements. As a result, 

a match is found unless all the matching conditions specified by the 

clauses are satisfied. The 

clause specifies the actions that are performed after 

the node match test concerning the attribute settings of the route information.

The comparisons of different nodes in a route policy uses a Boolean “OR” statement. 
The system examines the nodes in the route policy in sequence. Once the route is 
permitted by a single node in the route-policy, the route passes the matching test of 
the route policy without attempting the test of the next node.

The access control list (ACL) used by the route policy can be divided into three types: 
advanced ACL, basic ACL and interface ACL. 

A basic ACL is usually used for routing information filtering. When the user defines 
the ACL, the user must define the range of an IP address or subnet for the destination 
network segment address, or the next-hop address of the routing information. If an 
advanced ACL is used, perform the matching operation by the specified source 
address range.

For details of ACL configuration, refer to Chapter 7, Using QoS/ACL Commands.

The function of the IP Prefix is similar to that of the ACL, but it is more flexible and 
easier for users to understand. When the IP Prefix is applied to routing information 
filtering, its matching objects are the destination address information and the domain 
of the routing information. In addition, in the IP Prefix, you can specify the 

 

options and require it to receive only the routing information distributed by some 
certain routers. 

An IP Prefix is identified by the ip-prefix name. Each IP Prefix can include multiple list 
items, and each list item can specify the match range of the network prefix forms, 
and is identified with an index-number. The index-number designates the matching 
check sequence in the IP Prefix. 

During the matching, the router checks list items identified by the sequence-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 of the next list item.

Configuring a routing policy includes tasks described in the following sections:

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