Juniper BGP, Configuration Manual

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You can control the maximum number of received EBGP best paths that are
considered for path selection. The
external-paths command limits external route
target membership, thus controlling the number of EBGP peers that receive the route
target VPN routes referenced by the RT-MEM-NLRI route. BGP ignores routes received
from the peer after the limit specified with the
external paths command is reached.
Configuring Route-Target Filtering
To configure route-target filtering:
1.
Enable the BGP routing process in the specified AS.
The AS number identifies the PE router to other BGP routers.
host1(config)# router bgp 738
2.
Configure the peers for the BGP speaker. Use neighbor commands to specify
the PE router peers to which BGP advertises routes and to configure any additional
BGP attributes.
host1(config-router)# neighbor 10.2.2.2 remote-as 45
host1(config-router)# neighbor 10.2.2.2 update-source loopback 0
host1(config-router)# neighbor 10.2.2.2 next-hop-self
3.
Create the route-target address family to configure the router to use BGP signaling
to exchange the RT-MEM-NLRI attribute with peer routers.
Optionally, you can use the signaling keyword with the address-family command
when you configure the route-target address family to specify BGP signaling of
reachability information. Currently, you can omit the
signaling keyword with
no adverse effects.
host1(config-router)# address-family route-target signaling
4.
Activate the neighbors that routes of the route-target address family are
exchanged with for this BGP session. The neighbors must first be created in the
default IPv4 unicast address family.
host1(config-router-af)# neighbor 10.2.2.2 activate
host1(config-router-af)# neighbor 10.2.2.2 next-hop-self
5.
(Optional) Configure BGP to send a Default-MEM-NLRI route for all peers in the
address family or for a specific peer or peer group in the address family.
host1(config-router-af)# default-information originate
or
host1(config-router-af)#
neighbor 10.2.2.2 default-originate
6.
Set the maximum number of received external BGP paths that can be accepted
for route-target signaling.
host1(config-router-af)# external-paths 2
7.
Configure any additional address family parameters desired for the session.
external-paths
Constraining Route Distribution with Route-Target Filtering
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Chapter 5: Configuring BGP-MPLS Applications