Huawei Huawei Facebook This document specifies use of a set of IP tunnels to interconnect multiple network sites over IP backbone networks. The interconnected network sites form 'virtual' private network(s). The networks at any of those sites can be Layer 2 domains or/and Layer 3 subnets. The IP backbone networks that the tunnels traverse through can be IPv4 or IPv6. This document describes the special property (or features) that those IP tunnels need to have in order to interconnect multiple sites as if those sites are directly connected by wires.