Policy Framework Configuration Guide - Juniper Networks

Junos 10.4 Policy Framework Configuration Guide
How Prefix Lists Are Evaluated in Routing Policy Match Conditions
During prefix list evaluation, the policy framework software performs a longest-match
lookup, which means that the software searches for the prefix in the list with the longest
length. The order in which you specify the prefixes, from top to bottom, does not matter.
The software then compares a route’s source address to the longest prefix.
You can use prefix list qualifiers for prefixes contained in a prefix list by configuring a
prefix list filter. For more information, see Configuring Prefix Lists for Use in Routing Policy
Match Conditions.
If a match occurs, the evaluation of the current term continues. If a match does not occur,
the evaluation of the current term ends.
NOTE: If you specify multiple prefixes in the prefix list, only one prefix must
match for a match to occur. The prefix list matching is effectively a logical
OR operation.
Configuring Prefix List Filters
A prefix list filter allows you to apply prefix list qualifiers to a list of prefixes within a prefix
list. The prefixes within the list are evaluated using the specified qualifiers. You can
configure multiple prefix list filters under the same policy term.
To configure a prefix list filter, include the prefix-list-filter statement at the [edit
policy-options policy-statement policy-name from] hierarchy level:
[edit policy-options policy-statement policy-name]
from {
prefix-list-filter prefix-list-name match-type actions;
}
The prefix-list-name option is the name of the prefix list to be used for evaluation. You
can specify only one prefix list.
The match-type option is the type of match to apply to the prefixes in the prefix list. It
can be one of the match types listed in Table 20 on page 118.
The actions option is the action to take if the prefix list matches. It can be one or more of
the actions listed in “Configuring Flow Control Actions” on page 49 and “Configuring
Actions That Manipulate Route Characteristics” on page 49.
Table 20: Route List Match Types for a Prefix List Filter
Match Type
Match Condition
exact
The route shares the same most-significant bits (described by prefix-length), and prefix-length is equal
to the route’s prefix length.
longer
The route shares the same most-significant bits (described by prefix-length), and prefix-length is greater
than the route’s prefix length.
118
Copyright © 2010, Juniper Networks, Inc.