During the studying of MPLS VPN, we usually encounter the VPNv4 and Labeled BGP routes. A lot of people can't distinguish between them. Actually, they are so different from each other.
Before talking about the VPNv4 and the Labeled BFP routes, let's check the normal BGP route:
The VPNv4 route
The VPNv4 route is comprised of two parts: the IPv4 route and the route-distinguisher. The route-distinguisher is used to distinguish the different VPN-instances. The router can forward the VPNv4 route to the appropriate VPN-instance. When the BGP updates the VPNv4 route, the RD (route-distinguisher) will be contained in the MP_REACH_NLRI field, just as the picture below shows.
We noticed that a route-target value was attached in the EXTENDED_COMMUNITIES field. The route-target is used by the VPN-instance to decide whether the VPNv4 route will be accepted.
Labeled BGP route
Unlike the VPNv4 route, the Labeled BGP route is more similar to the normal BGP route. But the Labeled BGP route and the normal BGP route are also quite different.
In the Labeled BGP route, a MP_REACH_NLRI is attached as a VPNv4 BGP route does, but unlike the VPNv4 route, there is no RD or RT (route-target). It only carries a label stack, and the normal BGP route doesn't, just showing as the picture below:
The Labeled BGP route is used in MPLS VPN option C. Between the two ASBR, the labeled BGP route is transferred so that the label distributed by the different VPN-instances could pass through the different AS.
