Pim Policy Attach Points; Attached Policy Modification; Nonattached Policy Modification; Editing Routing Policy Configuration Elements - Cisco ASR 9000 Series Configuration Manual

Implementing Routing Policy

PIM Policy Attach Points

This section describes the PIM policy rpf-topology attach point and provides a summary of the PIM attributes
and operators.

Attached Policy Modification

Policies that are in use do, on occasion, need to be modified. In the traditional configuration model, a policy
modification would be done by completely removing the policy and reentering it. However, this model allows
for a window of time in which no policy is attached and default actions to be used, which is an opportunity
for inconsistencies to exist. To close this window of opportunity, you can modify a policy in use at an attach
point by respecifying it, which allows for policies that are in use to be changed, without having a window of
time in which no policy is applied at the given attach point.
A route policy or set that is in use at an attach point cannot be removed because this removal would result
Note
in an undefined reference. An attempt to remove a route policy or set that is in use at an attach point results
in an error message to the user.

Nonattached Policy Modification

As long as a given policy is not attached at an attach point, the policy is allowed to refer to nonexistent sets
and policies. Configurations can be built that reference sets or policy blocks that are not yet defined, and then
later those undefined policies and sets can be filled in. This method of building configurations gives much
greater flexibility in policy definition. Every piece of policy you want to reference while defining a policy
need not exist in the configuration. Thus, you can define a policy sample1 that references a policy sample2
using an apply statement even if the policy sample2 does not exist. Similarly, you can enter a policy statement
that refers to a nonexistent set.
However, the existence of all referenced policies and sets is enforced when a policy is attached. Thus, if a
user attempts to attach the policy sample1 with the reference to an undefined policy sample2 at an inbound
BGP policy using the statement neighbor 1.2.3.4 address-family ipv4 unicast policy sample1 in, the
configuration attempt is rejected because the policy sample2 does not exist.

Editing Routing Policy Configuration Elements

RPL is based on statements rather than on lines. That is, within the begin-end pair that brackets policy statements
from the CLI, a new line is merely a separator, the same as a space character.
The CLI provides the means to enter and delete route policy statements. RPL provides a means to edit the
contents of the policy between the begin-end brackets, using a text editor. The following text editors are
available on Cisco IOS XR software for editing RPL policies:
• Nano (default)
• Emacs
• Vim
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Attached Policy Modification
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