Cisco NCS 5500 Series

Default Drop Disposition
All route policies have a default action to drop the route under evaluation unless the route has been modified
by a policy action or explicitly passed. Applied (nested) policies implement this disposition as though the
applied policy were pasted into the point where it is applied.
Consider a policy to allow all routes in the 10 network and set their local preference to 200 while dropping
all other routes. You might write the policy as follows:
route-policy two
if destination in (10.0.0.0/8 ge 8 le 32) then
set local-preference 200
endif
end-policy
route-policy one
apply two
end-policy
It may appear that policy one drops all routes because it neither contains an explicit pass statement nor modifies
a route attribute. However, the applied policy does set an attribute for some routes and this disposition is
passed along to policy one. The result is that policy one passes routes with destinations in network 10, and
drops all others.
Control Flow
Policy statements are processed sequentially in the order in which they appear in the configuration. Policies
that hierarchically reference other policy blocks are processed as if the referenced policy blocks had been
directly substituted inline. For example, if the following policies are defined:
route-policy one
set weight 100
end-policy
route-policy two
set med 200
end-policy
route-policy three
apply two
set community (2:666) additive
end-policy
route-policy four
apply one
apply three
pass
end-policy
Policy four could be rewritten in an equivalent way as follows:
route-policy four-equivalent
set weight 100
set med 200
set community (2:666) additive
Routing Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.3.x
149
Implementing Routing Policy
Default Drop Disposition