Policy Statements; Remark; Disposition - Cisco NCS 5500 Series Configuration Manuals

Policy Statements

A drop in aggregation policy does not prevent generation of an aggregate, but it does prevent the current more
specific route from contributing to the aggregate. If another more specific route gives the route a pass, the
aggregate is generated. Only one more specific pass is required to generate an aggregate.
Policy Statements
Four types of policy statements exist: remark, disposition (drop and pass), action (set), and if (comparator).

Remark

A remark is text attached to policy configuration but otherwise ignored by the policy language parser. Remarks
are useful for documenting parts of a policy. The syntax for a remark is text that has each line prepended with
a pound sign (#):
# This is a simple one-line remark.
# This
# is a remark
# comprising multiple
# lines.
In general, remarks are used between complete statements or elements of a set. Remarks are not supported in
the middle of statements or within an inline set definition.
Unlike traditional !-comments in the CLI, RPL remarks persist through reboots and when configurations are
saved to disk or a TFTP server and then loaded back onto the router.

Disposition

If a policy modifies a route, by default the policy accepts the route. RPL provides a statement to force the
opposite—the drop statement. If a policy matches a route and executes a drop, the policy does not accept the
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
end-policy
!
Routing Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.3.x
152
set community (10:10)
apply B_rp
Implementing Routing Policy