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Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy on Cisco IOS XR Software
RC-384
Cisco IOS XR Routing Configuration Guide
OL-14356-01
Next-hop
The next-hop attach point provides increased control based on protocol and prefix-based match
operations. The attach point is typically used to decide whether to act on a next-hop notification (up or
down) event.
Support for next-hop tracking allows BGP to monitor reachability for routes in the Routing Information
Base (RIB) that can directly affect BGP prefixes. The route policy at the BGP next-hop attach point helps
limit notifications delivered to BGP for specific prefixes. The route policy is applied on RIB routes.
Typically, route policies are used in conjunction with next-hop tracking to monitor non-BGP routes.
The following example shows how to configure BGP nexthop tracking feature using a route policy to
monitor static or connected routes with the prefix 20.0.0.0 and prefix length 8.
route-policy nxthp_policy_A
if destination in (20.0.0.0/8) and protocol in (static, connected) then
pass
endif
end-policy
router bgp 2
address-family ipv4 unicast
nexthop route-policy nxthp_policy_A
.
.
.
Clear-Policy
The clear-policy attach point provides increased control based on various AS path match operations
when using a clear bgp command. This attach point is typically used to decide whether to clear BGP
flap statistics based on AS-path-based match operations.
The following example shows how to configure a route policy where the in operator evaluates to true if
one or more of the regular expression matches in the set my-as-set successfully match the AS path associated
with the route. If it is a match, then the clear command clears the associated flap statistics.
as-path-set my-as-set
ios-regex '_12$',
ios-regex '_13$'
end-set
route-policy policy_a
if as-path in my-as-set then
pass
else
drop
endif
end-policy
clear bgp ipv4 unicast flap-statistics route-policy policy_a
Debug
The debug attach point provides increased control based on prefix-based match operations. This attach
point is typically used to filter debug output for various BGP commands based on the prefix of the route.
The following example shows how to configure a route policy that will only pass the prefix 20.0.0.0 with
prefix length 8; therefore, the debug output shows up only for that prefix.
route-policy policy_b
if destination in (20.0.0.0/8) then