A tunneling protocol used for secure node-to-node communications by Internet service providers (ISPs) and other virtual private network (VPN) service providers in support of multiple, simultaneous tunnels in the network core. End users gain access to the service provider on an unencrypted basis, with the service provider assuming the responsibility for encryption at the edge of the packet network. L2TP is an extension to the Point-to-Point Protocol (PPP) that evolved from a combination of Microsoft's PPTP and Cisco's Layer 2 Forwarding (L2F) protocol. L2TP is described in IETF RFC 2661. See also encryption, ISP, PPP, PPTP, protocol, tunneling, and VPN.
(Layer 2 Tunneling Protocol) A protocol from the IETF that lets remote users access the corporate network. L2TP allows a PPP session to travel over multiple links and networks. PPP is used to encapsulate IP packets from the user's PC or mobile device to the ISP, and L2TP extends that session across the Internet. L2TP was derived from Microsoft's Point-to-Point Tunneling Protocol (PPTP) and Cisco's Layer 2 Forwarding (L2F) technology. See PPTP and L2F. From Access Concentrator to Network Server The "L2TP Access Concentrator" (LAC) encapsulates PPP frames with L2TP headers and sends them over the Internet as UDP packets (or over an ATM, frame relay or X.25 network). At the other end, the "L2TP Network Server" (LNS) terminates the PPP session and hands the IP packets to the LAN. L2TP software can also be run in the user's PC. Carriers also use L2TP to offer remote points of presence (POPs) to smaller ISPs. Users in remote locations dial into the carrier's local modem pool, and the carrier's LAC forwards L2TP traffic to the ISP's LNS. L2TP and IPsec L2TP does not include encryption (as does PPTP), but is often used with IPsec in order to provide virtual private network (VPN) connections from remote users to the corporate LAN. See PPP, virtual private network and IPsec.