Cisco Systems The Layer 2 Tunneling Protocol (L2TPv3) provides a standard method for setting up and managing L2TP sessions to tunnel a variety of L2 protocols. One of the reference models supported by L2TPv3 describes the use of an L2TP session to cross-connect two Layer 2 circuits attached to a pair of peering LACs. A cross-connect is a basic form of Layer 2 Virtual Private Networks (L2VPNs). This document describes mechanisms which utilize the building blocks that L2TP provides to construct different types of L2VPNs.