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Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
RC-221
Cisco IOS XR Routing Configuration Guide
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