3com 8807 User Guide

When a router advertises or receives routing information, it possibly needs to 
implement some policies to filter the routing information, so as to receive or 
advertise the routing information which can meet the specified condition only. A 
routing protocol, e.g. RIP, may 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.

For implementing the routing policy, you need define a set of matching rules by 
specifying the characteristics of the routing information to be filtered. You can set 
the rules based on such attributes like 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 the route information.

In Switch 8800 Family series, five kinds of filters, Route-policy, ACL, AS-path, 
Community-list, and IP-prefix, are provided to be called by the routing protocols. 
The following sections introduce these filters respectively.

The access control list (ACL) used by routing policy can be divided into the 
following types:

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Number-based basic ACLs

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Name-based basic ACLs

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Number-based advanced ACLs

■

Name-based advanced ACLs

■

Number-based L2 ACLs

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Name-based L2 ACLs

For routing information filtering, the basic ACL is generally used. When users 
define the ACL, they will define the range of an IP address or subnet to 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.

The function of the IP-prefix is similar to that of ACL, but it is more flexible and 
easy for the users to understand. When the IP-prefix is applied to the routing 
information filtering, its matching objects are the destination address information 
domain of the routing information.