3com 3031 Instruccion De Instalación

When a router distributes or receives routing information, it possibly needs to 
implement some policies to filter the routing information, so as to receive or 
distribute the routing information which can meet the specified condition only. A 
routing protocol, e.g. RIP, maybe need import the routing information discovered 
by other protocols to enrich its routing knowledge. While importing the routing 
information, it possibly only needs import the information meeting the conditions 
and set some special attributes to make them meet its requirement.

To implement the routing policy, you need define a set of matching rules by 
specifying the characteristics of the routing information in the routing policy under 
implementation. You can set the rules based on such attributes as destination 
address and source address of the information. The matching rules can be set in 
advance and then used in the routing policy to advertise, receive and import 
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 import. The following 
will introduce each kind of filter respectively.

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

A route policy can comprise multiple nodes. Each node is a unit for matching test, 
and the nodes will be matched on the basis of their node numbers. Each node 
comprises a set 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-match clauses on the same node is in logic AND relationship. Only 
when the matching requirements specified by all the if-match clauses on a node 
are satisfied, can the matching test on the node be passed. The apply clause 
specifies the actions performed after the node matching test, concerning the 
attribute settings of the routing information.

The different nodes of a route-policy is in logic OR relationship. The system will 
check each node of route-policy one by one. Once the test on a route-policy node 
is passed, it indicates the matching test of the route-policy is passed (the test on 
the next-node will not proceed).

There are three kinds of ACLs: advanced represents advanced ACL, basic 
represents basic ACL and interface represents interface-based ACL.