Juniper JUNOSE 11.2.X BGP AND MPLS, Configuration Manual

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Figure 86: Site Connectivity in an Overlapping VPN
Figure 87 on page 412 shows how to configure the VRF import and export route targets
to build an overlapping VPN. In this example, the export and import route targets are
different for VPN A and VPN B. Therefore, VPN A does not accept routes from VPN B and
VPN B does not accept routes from VPN A.
The import route target list for the overlapping VPN AB includes both 100:10 and 100:20.
VPN AB can therefore accept routes advertised by any site in either VPN A or VPN B.
Because the VPN AB export route target list also includes both 100:10 and 100:20, every
route advertised by VPN AB can be accepted by any site in either VPN A or VPN B.
Figure 87: Route Target Configuration for an Overlapping VPN
An interesting special case of an overlapping VPN is when two VRFs on the same PE router
belong to the same VPN as shown in Figure 88 on page 413. The configuration of the VRF
import and export route targets is the same as for the example in Figure 87 on page 412.
If the export route target of one VRF (for example, the VPN AB VRF) matches the import
route target of another VRF (for example, the VPN A VRF), then BGP routes are exported
from one VRF to the other VRF; in this case from the VPN AB VRF to the VPN A VRF.
Consequently, traffic that arrives in one VRF is forwarded out another VRF without going
through the MPLS core network.
Copyright © 2010, Juniper Networks, Inc. 412
JunosE 11.2.x BGP and MPLS Configuration Guide