3Com 10014298 IP Routing Policy, Information that meets its conditions, IP Prefix, Route Policy

IP Routing Policy 99

IP Routing Policy	When a router distributes or receives routing information, it needs to implement
	policies to filter the routing information so it can receive or distribute the routing
	information that meets only the specified condition. A routing protocol such as RIP
	may need to import routing information discovered by other protocols to enrich its
	routing knowledge. While importing the routing information, it must import only
	the information that meets its conditions.
	To implement the routing policy, you must define a set of rules by specifying the
	characteristics of the routing information to be filtered. You can set the rules
	based on such attributes as destination address and source address of the
	information. The rules can be set in advance and then used in the routing policy to
	advertise, receive, and import the route information.

Configuring IP Routing Policy is described in the following sections:

■Routing Information Filters

■Configuring an IP Routing Policy

■Troubleshooting Routing Policies

■Configuring Route Capacity

Routing Information The Switch 7750 supports four kinds of filters, route-policy, acl, ip-prefix, and

Filters community-list. The following sections introduce these filters:

■Route Policy

■ACL

■IP Prefix

Route Policy

A route map is used for matching some attributes with given routing information and the attributes of the information will be set if the conditions are satisfied.

A route map can include multiple nodes. Each node is a unit for match testing, and the nodes are matched in a sequence-number-based order. Each node includes a set of if-match and apply clauses. The if-match clauses define the matching rules and the matching objects are attributes of routing information. The comparison of if-match clauses for a node uses a series of Boolean and statements. As a result, a match is found if all the matching conditions specified by the if-match clauses are satisfied. The apply clause specifies the actions that are performed after the node match test concerning the attribute settings of the route information.

The comparison 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.

ACL

The access control list (ACL) used by the route policy can be divided into three types: advanced ACL, basic ACL, and Layer-2 ACL.