3Com Switch 8800 Advanced Software V5 Configuration Guide

Routing Policy Configuration Task List 245
order of node sequence number. Once a node is matched, the routing policy is
passed and the packet will not go through the next node.
Each node comprises a list of if-match and apply clauses. The if-match clauses
define the match criteria. The matching objects are some attributes of routing
information. The different if-match clauses on a node is in logical AND
relationship. Only when the matching conditions specified by all the if-match
clauses on the node are satisfied, can routing information pass the node. The
apply clauses specify the actions performed after the node is passed, concerning
the attribute settings for routing information.
Routing Policy
Application
A routing policy is applied in two ways:
■ When redistributing routes from other routing protocols, a routing protocol
accepts only routes passing the routing policy.
■ When receiving or advertising routing information, a routing protocol uses the
routing policy to filter routing information.
Routing Policy
Configuration Task
List
To configure a routing policy, perform the tasks described in the following
sections:
Defining Filtering Lists
Prerequisites Before configuring this task, you need to decide on:
■ IP-prefix list name
■ Matching address range
■ Extcommunity list sequence number
Defining an IP-prefix List Define an IPv4 prefix list
Identified by name, each IPv4 prefix list can comprise multiple items. Each item
specifies a matching address range in the form of network prefix identified by
index number.
During matching, the system compares the route to each item identified by index
number in the ascending order. If one item matches, the route passes the IP-prefix
list, without needing to match against the next item.
To define an IPv4 prefix list, use the following commands:
Task
“Defining Filtering Lists” on
page 245
“Defining an IP-prefix List” on page 245
“Defining an AS Path ACL” on page 247
“Defining a Community List” on page 247
“Defining an Extended Community List” on page 247
“Configuring a Routing
Policy” on page 247
“Creating a Routing Policy” on page 248
“Defining if-match Clauses for the Routing Policy” on page
248
“Defining apply Clauses for the Routing Policy” on page 250