Figure 88: Overlapping VPNs on a Single PE
From a given CE router you can ping the local address of any VRF that has a VPN
overlapping another VPN to which the CE router belongs.
To achieve this internally, the router obtains the source address as follows:
•
If the next-hop interface is in the same VRF and the interface is numbered, the router
uses the source address of the interface.
•
If the next-hop interface is in the same VRF and the interface is unnumbered, the router
uses either the source address of the interface it is pointing to or the router ID of the
VRF.
•
If the next-hop interface is in a different VRF, the router uses the source address of the
VRF. If the router does not have a router ID value, the packet is discarded.
NOTE: The source address of the transmit interface is not used as the source address
of the packet.
Constraining Route Distribution with Route-Target Filtering
In typical BGP configurations, you can use cooperative route filtering to reduce the amount
of processing required for inbound BGP updates and the amount of BGP control traffic
generated by BGP updates. Cooperative route filtering works by having the remote peer
install a BGP speaker’s inbound route filter as its own outbound route filter. This filtering
causes the remote peer to advertise only those routes that the local peer can accept.
For BGP/MPLS VPNs, route-target filtering is a better approach. Route-target filtering
controls the distribution of BGP routes based on the VPNS (indicated by the route-target
extended communities) to which peer routers belong. PE routers use the MP_REACH_NLRI
413Copyright © 2010, Juniper Networks, Inc.
Chapter 6: Configuring BGP-MPLS Applications
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