Origin of route explosion in virtual private networks

Enterprises often have sites that are spread in distant locations. These sites need to interconnect with the same level of privacy as in a local-area network. Virtual Private Networks (VPNs) were introduced to serve this need. A common VPN technology uses Multiprotocol extensions for the Border Gateway Protocol (MP-BGP) and Multiprotocol Label Switching (MPLS). This technology allows a service provider to share its IP backbone among multiple VPN clients while preserving privacy. MPLS tunnels provide traffic isolation, whereas MP-BGP distributes VPN routes. Despite the wide deployment of BGP/MPLS VPNs[1], there have been only few studies to understand their behavior, mostly because of the lack of public data. Prior work focused on BGP convergence [3] and on integrity constraints to ensure connectivity [2].