Introduction
The Layer 2 Tunneling Protocol version 3 (L2TPv3) provides a mean to interconnect transparently at high speed and at Layer 2 level a pair of interfaces through a Packet Switched Network (for instance an IPv4 based network).
It can be used to build a multitude of L2 based services like VLL, L2 PPVPN, etc.
A pre-standard Cisco implementation was called UTI (Universal Transport Interface).
L2TPv3 is described in details in draft-ietf-l2tpext-l2tp-base-02.txt