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
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
pass
endif
end-policy
router bgp 2
neighbor 10.0.0.1
remote-as 3
address-family ipv4 unicast
default-originate policy sample-originate
.
.
.
Neighbor Export
The neighbor export attach point selects the BGP routes to send to a given peer or group of peers. The routes
are selected by running the set of possible BGP routes through the associated policy. Any routes that pass the
policy are then sent as updates to the peer or group of peers. The routes that are sent may have had their BGP
attributes altered by the policy that has been applied.
The following policy sends all BGP routes to neighbor 10.0.0.5. Routes that are tagged with any community
in the range 2:100 to 2:200 are sent with a MED of 100 and a community of 2:666. The rest of the routes are
sent with a MED of 200 and a community of 2:200.
route-policy sample-export
if community matches-any (2:[100-200]) then
set med 100
set community (2:666)
else
set med 200
set community (2:200)
Routing Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.3.x
158
Implementing Routing Policy
Additional-Path
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