Cisco ASR 9000 Series Routing Configuration Manual page 594

Policy Statements
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
pass
drop
pass
end-policy
When one policy applies another, it is as if the applied policy were copied into the right place in the applying
policy, and then the same drop-and-pass semantics are put into effect. For example, policies ONE and TWO
are equivalent to policy ONE-PRIME:
route-policy ONE
apply two
if as-path neighbor-is '123' then
pass
endif
end-policy
route-policy TWO
if destination in (10.0.0.0/16 le 32) then
drop
endif
end-policy
route-policy ONE-PRIME
if destination in (10.0.0.0/16 le 32) then
drop
endif
if as-path neighbor-is '123' then
pass
endif
end-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
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
564
Implementing Routing Policy