Sun Microsystems Cisco Systems VPNet Technologies IBM Corporation The L2TP document [1] defines the base protocol which describes the method of tunneling PPP [2] data. The L2TP document states that the security mechanism used over an IP network is to use the IETF's IPSEC protocols. L2TP was designed in such a way as to be able to run over any underlying layer (i.e. Frame Relay, ATM, etc.). This document specifies extensions to the L2TP protocol in order to provide authentication and integrity of individual packets in a tunneled session over a network where IPSEC or another suitable security protocol is not available.