Ip Routing Policy Overview; Chapter 5 Ip Routing Policy Configuration - Huawei Quidway S3900 Series Operation Manual

Operation Manual – Routing Protocol
Quidway S3900 Series Ethernet Switches-Release 1510

Chapter 5 IP Routing Policy Configuration

5.1 IP Routing Policy Overview

When a router distributes or receives routing information, it may need to implement
some policies to filter the routing information, so as to receive or distribute only the
routing information meeting given conditions. A routing protocol (RIP, for example)
may need to import the routing information discovered by other protocols to enrich its
routing knowledge. While importing routing information from another protocol, it
possibly only needs to import the routes meeting given conditions and set some
attributes of the imported routes to make the routes meet the requirements of this
protocol.
For the implementation of a routing policy, you need to 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 as destination address and source address of the
information. The matching rules can be set in advance and then used in the routing
policies to advertise, receive, and import routes.
The S3900 series provide three kinds of filters (Route-policy, ACL, and ip-prefix),
which can be referenced by routing protocols. The following sections introduce these
filters.
I. Route-policy
A route policy is used to match some attributes with 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 in the order 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 relationship
among the if-match clauses for a node is "AND". As a result, a matching test against
a node is successful only when all the matching conditions specified by the if-match
clauses in the node are satisfied. The apply clauses specify the actions performed
after a matching test against the node is successful, and the actions can be the
attribute settings of routing information.
The relationships among different nodes in a route-policy are "OR". As a result, the
system examines the nodes in the route-policy in sequence, and once the route
passes a node in the route-policy, it will pass the matching test of the route-policy
without entering the test of the next node.
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Chapter 5 IP Routing Policy Configuration