BGP performance analysis for large scale VPN

Large enterprises often have sites that are spread in distant locations. These scattered sites need to interconnect with the same level of security and privacy as in a local area network. Virtual Private Networks (VPNs) were used to serve this need. A common VPN topology was composed of Multiprotocol extensions for the Border Gateway Protocol (MP-BGP) and Multiprotocol Label Switching (MPLS). This technology preserves privacy among multiple VPN via MPLS tunnels traffic isolation, whereas BGP distributes VPN route informations. Despite the wide deployment of BGP MPLS VPNs, the disadvantages of this VPN technology gradually be exposed with the VPN scale expanding.We have a study to the behavior of a large scale VPN. A simple analysis shows that slow routes convergence and slow route table transfer is the main reason. Slow routes convergence makes a increasing time to update exchange update routes between routers, meanwhile, Slow route table transfer leads to a lower utilization of provider backbone.