Juniper BGP, Configuration Manual

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Figure 90: Hub-and-Spoke VPN
Route-target configuration on PE 2:
host2(config)# virtual-router boston
host2:boston(config)# ip vrf vrfC
host2:boston(config-vrf)# route-target export 777:50
host2:boston(config-vrf)# route-target import 777:25
Route-target configuration on PE 3:
host3(config)# ip vrf vrfE
host3(config-vrf)# route-target export 777:50
host3(config-vrf)# route-target import 777:25
This configuration ensures that when VRF E on PE 3 receives an update message
from PE 1, BGP installs the advertised route only if it has a route target of 25. Routes
from PE 2 have a route target of 50, and cannot be installed. Similarly, when VRF C
on PE 2 receives an update message from PE 1, BGP installs the advertised route
only if it has a route target of 25. Routes from PE 3 have a route target of 50, and
cannot be installed. When PE 1 receives updates from either PE 2 or PE 3, the routes
have a route target of 50, match VRF A’s import list, and are installed in VRF A’s
forwarding table.
Setting Import and Export Maps for a VRF
The combination of the route-target export list of VRF A and the route-target import
list of VRF B determines whether routes from VRF A are distributed to VRF B. You
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Configuring BGP VPN Services
JUNOSe 11.1.x BGP and MPLS Configuration Guide