LT2P
Short for Layer 2 Tunneling Protocol, L2TP is a tunneling protocol that is used with a Virtual Private Network (VPN). It is a Session Layer protocol, using the UDP port 1701. L2TP does not include any encryption and relies on other encryption methods to provide data security and privacy. IPsec is often used with L2TP to provide this security and privacy.
L2TP can be used as a tunneling mechanism to resell ADSL connectivity, by cable providers to resell connectivity, and by companies providing a connection for their employees to connect to their private network from outside the office.
Also see: Network definitions, Protocol