Layer Two Tunneling Protocol An industry-standard Internet tunneling protocol that provides encapsulation for sending Point-to-Point Protocol (PPP) frames across packet-oriented media. For IP networks, L2TP traffic is sent as User Datagram Protocol (UDP) messages. In Microsoft operating systems, L2TP is used in conjunction with Internet Protocol security (IPSec) as a virtual private network (VPN) technology to provide remote access or router-to-router VPN connections. L2TP is described in RFC 2661