Cisco Systems IOS XR manual Parameterization, RC-214

Implementing Routing Policy on Cisco IOS XR Software

Information About Implementing Routing Policy

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-policyname 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’ 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 before it is received. If a route that has autonomous system 1234 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' 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

This parameterized policy can then be reused with different parameterizations, as shown in the following example. In this manner, policies that share a common structure but use different values in some of their individual statements can be modularized. For details on which attributes can be parameterized, see the individual attribute sections.

Cisco IOS XR Routing Configuration Guide

RC-214