Policy Framework Configuration Guide - Juniper Networks

CHAPTER 5
Extended Match Conditions Configuration
This chapter describes how to configure extended match conditions:
• Configuring AS Path Regular Expressions to Use as Routing Policy Match
Conditions on page 95
• Overview of BGP Communities and Extended Communities as Routing Policy Match
Conditions on page 102
• Defining BGP Communities and Extended Communities for Use in Routing Policy Match
Conditions on page 104
• Including BGP Communities and Extended Communities in Routing Policy Match
Conditions on page 110
• How BGP Communities and Extended Communities Are Evaluated in Routing Policy
Match Conditions on page 110
• Using Routing Policies to Prevent Advertisement of BGP Communities to
Neighbors on page 111
• Examples: Configuring BGP Communities as Routing Policy Match Conditions on page 111
• Configuring Prefix Lists for Use in Routing Policy Match Conditions on page 116
• Example: Configuring a Prefix List on page 119
• Configuring Route Lists for Use in Routing Policy Match Conditions on page 119
• Configuring Subroutines in Routing Policy Match Conditions on page 128
• Configuring Routing Policy Match Conditions Based on Routing Table Entries on page 132
Configuring AS Path Regular Expressions to Use as Routing Policy Match Conditions
A BGP AS path is a path to a destination. An AS path consists of the AS numbers of
networks that a packet traverses if it takes the associated route to a destination. The AS
numbers are assembled in a sequence, or path, that is read from right to left. For example,
for a packet to reach a destination using a route with an AS path 5 4 3 2 1, the packet first
traverses AS 1 and so on until it reaches AS 5, which is the last AS before its destination.
You can define a match condition based on all or portions of the AS path. To do this, you
create a named AS path regular expression and then include it in a routing policy.
Copyright © 2010, Juniper Networks, Inc.
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