Proper noun
L2TP
layer two tunnelling protocol
They also will require authorization for any type of Virtual Private Network (VPN) technology (for example; PPTP, L2TP, GRE Tunneling, OpenVPN, and most other protocols that allow you protect your information). Source: Internet
L2TP can be used to provide these interfaces, this technique is called L2TP/IPsec. Source: Internet
L2TP carries PPP frames inside transport packet. Source: Internet