Cisco Systems IOS XR manual Action, RC-221

Implementing Routing Policy on Cisco IOS XR Software

Information About Implementing Routing Policy

Because the effect of an explicit drop statement is immediate, routes in 10.0.0.0/16 le 32 are dropped without any further policy processing. Other routes are then considered to see if they were advertised by autonomous system 123. If they were advertised, they are passed; otherwise, they are implicitly dropped at the end of all policy processing.

Action

An action is a sequence of primitive operations that modify a route. Most actions, but not all, are distinguished by the set keyword. In a route policy, actions can be grouped together. For example, the following is a route policy comprising three actions:

route-policy actions

set med 217

set community (12:34) additive delete community in (12:56)

end-policy

If

In its simplest form, an if statement uses a conditional expression to decide which actions or dispositions should be taken for the given route. For example:

if as-path in as-path-set-1 then drop

endif

The example indicates that any routes whose AS path is in the set as-path-set-1 are dropped. The contents of the then clause may be an arbitrary sequence of policy statements.

The following example contains two action statements:

if origin is igp then

set med 42

prepend as-path 73 5 endif

The CLI provides support for the exit command as an alternative to the endif command.

The if statement also permits an else clause, which is executed if the if condition is false:

if med eq 8 then

set community (12:34) additive else

set community (12:56) additive

endif

The policy language also provides syntax, using the elseif keyword, to string together a sequence of tests:

if med eq 150 then

set local-preference 10 elseif med eq 200 then

set local-preference 60 elseif med eq 250 then

set local-preference 110 else

set local-preference 0 endif

Cisco IOS XR Routing Configuration Guide

RC-221