Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?


Traffic Protection Using L2TP Tunneling Protocol Overview


Layer 2 Tunneling Protocol (L2TP) is another tunneling protocol used to transmit data securely across the Internet. Because L2TP can transport Point to Point Protocol (PPP) frames over IP, it is often used to:

  • Establish PPP connections (For example, authenticate ADSL services using PPP for users with an ISP at the opposite side of a Telco IP/ATM network

  • Transmit non-IP protocols (For example, bridge Novell and other network protocols)

PPP can send IP datagrams over a serial link, and it is often used to enable dial-up users to connect to their ISP and to the Internet. PPP authenticates username and password, and assigns parameters such as IP address, IP gateway, and DNS. PPP can also tunnel non-IP traffic across a serial link, such as Novell IPX or Appletalk.

PPP is also useful because it can carry non-IP traffic and authenticate connections to RADIUS servers. However, because PPP is not an IP protocol, Internet routers and switches cannot route PPP packets. To route PPP packets, you use L2TP, which encapsulates PPP packet inside an Internet routable, UDP packet. L2TP VPNs support remote access service users using Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP) authentication.

Using L2TP over AutoKey IKE

L2TP only transmits packets; for encryption, authentication, or other data protection services, you must further encapsulate the L2TP packet using AutoKey IKE.