Filter
Top Products
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
RC-215
Cisco IOS XR Routing Configuration Guide
route-policy origin-10
if as-path originates-from ‘10’ then
apply param-example(10)
else
pass
endif
end-policy
route-policy origin-20
if as-path originates-from ‘20’ then
apply param-example(20)
else
pass
endif
end-policy
The parameterized policy param-example provides a policy definition that is expanded with the values
provided as the parameters in the apply statement. Note that the policy hierarchy is always maintained,
Thus, if the definition of param-example changes, then the behavior of origin_10 and origin_20 changes
to match.
The effect of the origin-10 policy is that it adds the community 1234:10 to all routes that pass through
this policy and have an AS path indicating the route originated from autonomous system 10. The
origin-20 policy is similar except that it adds to community 1234:20 for routes originating from
autonomous system 20.
Semantics of Policy Application
This section discusses how routing policies are evaluated and applied. The following concepts are
discussed:
• Boolean Operator Precedence, page RC-215
• Multiple Modifications of the Same Attribute, page RC-216
• When Attributes Are Modified, page RC-216
• Default Drop Disposition, page RC-217
• Control Flow, page RC-217
• Policy Verification, page RC-218
Boolean Operator Precedence
Boolean expressions are evaluated in order of operator precedence, from left to right. The highest
precedence operator is not, followed by and, and then or. The following expression:
med eq 10 and not destination in (10.1.3.0/24) or community matches-any ([10..25]:35)
if fully parenthesized to display the order of evaluation, would look like this:
(med eq 10 and (not destination in (10.1.3.0/24))) or community matches-any ([10..25]:35)
The inner not applies only to the destination test; the and combines the result of the not expression with
the Multi Exit Discriminator (MED) test; and the or combines that result with the community test. If the
order of operations are rearranged:
not med eq 10 and destination in (10.1.3.0/24) or community matches-any ([10..25]:35)