10.6. COMPARISON OF PIM/GRE AND BGP/MPLS mVPNS
As mentioned in the beginning of the chapter, the L3VPN IETF working group draft on multicast support, [VPN-MCAST] covers both the PIM/GRE (draft-rosen) and the BGP/MPLS (NG) approaches, and deployments of draft-rosen exist in several large networks. Having described both solutions in this chapter, let us compare them by looking at (a) the VPN model implemented by each of the solutions, (b) the control-plane protocol used in each case, (c) the data-plane mechanisms, (d) the operation in an inter-AS scenario and (e) deployment considerations for a service provider. Each of these aspects will be examined separately below.
10.6.1. VPN model used
Some of the most significant differences between the two solutions are rooted in the underlying VPN models used: the Virtual Router model, used by the PIM/GRE solution, and the Aggregated Routing model, used by the BGP/MPLS solution. Therefore, in order to better understand the differences between the two approaches, let us first examine the differences between the two models.
In the Virtual Router model, the exchange of VPN routing information among PEs is accomplished by operating separate instances of routing protocols among the PEs, one instance for each VPN. The exchange of VPN data traffic among PEs is accomplished by setting up VPN-specific tunnels between PE devices, where logically these tunnels are between the VRFs which are within the PE devices. These tunnels are used as if they ...
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