Cisco ASR 9000 Series Configuration Manual page 515

Implementing Routing Policy
route. If a policy does not modify the route, by default the route is dropped. To prevent the route from being
dropped, the pass statement is used.
The drop statement indicates that the action to take is to discard the route. When a route is dropped, no further
execution of policy occurs. For example, if after executing the first two statements of a policy the drop
statement is encountered, the policy stops and the route is discarded.
Note All policies have a default drop action at the end of execution.
The pass statement allows a policy to continue executing even though the route has not been modified. When
a policy has finished executing, any route that has been modified in the policy or any route that has received
a pass disposition in the policy, successfully passes the policy and completes the execution. If route policy
B_rp is applied within route policy A_rp, execution continues from policy A_rp to policy B_rp and back to
policy A_rp provided prefix is not dropped by policy B_rp.
route-policy A_rp
set community (10:10)
apply B_rp
end-policy
!
route-policy B_rp
if destination in (121.23.0.0/16 le 32, 155.12.0.0/16 le 32) then
set community (121:155) additive
endif
end-policy
!
By default, a route is dropped at the end of policy processing unless either the policy modifies a route attribute
or it passes the route by means of an explicit pass statement. For example, if route-policy B is applied within
route-policy A, then execution continues from policy A to policy B and back to policy A, provided the prefix
is not dropped by policy B.
route-policy A
if as-path neighbor-is '123' then
apply B
policy statement N
end-policy
Whereas the following policies pass all routes that they evaluate.
route-policy PASS-ALL
pass
end-policy
route-policy SET-LPREF
set local-preference 200
end-policy
In addition to being implicitly dropped, a route may be dropped by an explicit drop statement. Drop statements
cause a route to be dropped immediately so that no further policy processing is done. Note also that a drop
statement overrides any previously processed pass statements or attribute modifications. For example, the
following policy drops all routes. The first pass statement is executed, but is then immediately overridden by
the drop statement. The second pass statement never gets executed.
route-policy DROP-EXAMPLE
OL-30423-03
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.1.x
Policy Statements
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