Cisco ASR 9000 Series Routing Configuration Guide

Policy Definitions
Policy definitions create named sequences of policy statements. A policy definition consists of the CLI
route-policy keyword followed by a name, a sequence of policy statements, and the end-policy keyword.
For example, the following policy drops any route it encounters:
route-policy drop-everything
drop
end-policy
The name serves as a handle for binding the policy to protocols. To remove a policy definition, issue the no
route-policy name command.
Policies may also refer to other policies such that common blocks of policy can be reused. This reference to
other policies is accomplished by using the apply statement, as shown in the following example:
route-policy check-as-1234
if as-path passes-through ‘1234.5’ then
apply drop-everything
else
pass
endif
end-policy
The apply statement indicates that the policy drop-everything should be executed if the route under
consideration passed through autonomous system 1234.5 before it is received. If a route that has autonomous
system 1234.5 in its AS path is received, the route is dropped; otherwise, the route is accepted without
modification. This policy is an example of a hierarchical policy. Thus, the semantics of the apply statement
are just as if the applied policy were cut and pasted into the applying policy:
route-policy check-as-1234-prime
if as-path passes-through '1234.5' then
drop
else
pass
endif
end-policy
You may have as many levels of hierarchy as desired. However, many levels may be difficult to maintain and
understand.
Parameterization
In addition to supporting reuse of policies using the apply statement, policies can be defined that allow for
parameterization of some of the attributes. The following example shows how to define a parameterized policy
named param-example. In this case, the policy takes one parameter, $mytag. Parameters always begin with
a dollar sign and consist otherwise of any alphanumeric characters. Parameters can be substituted into any
attribute that takes a parameter.
In the following example, a 16-bit community tag is used as a parameter:
route-policy param-example ($mytag)
set community (1234:$mytag) additive
end-policy
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
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Implementing Routing Policy
Policy Definitions

Cisco ASR 9000 Series Specifications

General

Brand	Cisco
Model	ASR 9000 Series
Category	Network Router
Language	English