3com 10014299 Betriebsanweisung

This chapter covers the following topics:

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During the information exchange with a peer router, the routing protocol may 
need to receive or distribute only part of the route information that complies with 
specific conditions; and to import only part of the route information learned by 
other protocols that satisfy the preset conditions. In addition, some attributes of 
the imported route information are set in order to satisfy the requirements of the 
protocol. The route strategy also provides measures for the routing protocol to 
implement these functions.

The route strategy consists of a series of rules, classified into three types and used 
for route information filtering in route advertisement, route receiving, and route 
import. Since defining a strategy is similar to defining a group of filters that are 
used during receiving or advertising route information or before the route 
information exchange between different protocols, route strategy is also called 
route filtering.

A common filter is the basis for route strategy implementation. The user defines 
some matching conditions as necessary, which are referred to when making the 
routing strategies. Apply these conditions to different objects such as the 
destination address of the routing information, and the router address publishing 
the routing information, to implement route information filtering.

A routing strategy provides five filters: 

1 Routing policy

2 Access list

3 Aspath-list

4 Community-list 

5 Prefix-list

These filters serve as the reference for the protocols to work out routing strategies.