Bgp Policy Attach Points; Additional-Path; Dampening; Default Originate - Cisco ASR 9000 Series Configuration Manual

Attach Points

BGP Policy Attach Points

This section describes each of the BGP policy attach points and provides a summary of the BGP attributes
and operators.

Additional-Path

The additional-path attach point provides increased control based on various attribute match operations. This
attach point is used to decide whether a route-policy should be used to select additional-paths for a BGP
speaker to be able to send multiple paths for the prefix.
The add path enables BGP prefix independent convergence (PIC) at the edge routers.
This example shows how to set a route-policy "add-path-policy" to be used for enabling selection of additional
paths:
router bgp 100
address-family ipv4 unicast
additional-paths selection route-policy add-path-policy

Dampening

The dampening attach point controls the default route-dampening behavior within BGP. Unless overridden
by a more specific policy on the associate peer, all routes in BGP apply the associated policy to set their
dampening attributes.
The following policy sets dampening values for BGP IPv4 unicast routes. Those routes that are more specific
than a /25 take longer to recover after they have been dampened than routes that are less specific than /25.
route-policy sample_damp
if destination in (0.0.0.0/0 ge 25) then
set dampening halflife 30 others default
else
set dampening halflife 20 others default
endif
end-policy
router bgp 2
address-family ipv4 unicast
bgp dampening route-policy sample_damp
.
.
.

Default Originate

The default originate attach point allows the default route (0.0.0.0/0) to be conditionally generated and
advertised to a peer, based on the presence of other routes. It accomplishes this configuration by evaluating
the associated policy against routes in the Routing Information Base (RIB). If any routes pass the policy, the
default route is generated and sent to the relevant peer.
The following policy generates and sends a default-route to the BGP neighbor 10.0.0.1 if any routes that match
10.0.0.0/8 ge 8 le 32 are present in the RIB.
route-policy sample-originate
if rib-has-route in (10.0.0.0/8 ge 8 le 32) then
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pass
Implementing Routing Policy
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