Internet & Intranet Security

13.4 LAYER 2 TUNNELING PROTOCOL

In June 1996, Microsoft and Cisco Systems proposed and submitted a combination of MS-PPTP and the L2F protocol to the IETF PPPEXT WG. The proposal was named Layer 2 Tunneling Protocol (L2TP) [18]. This collaborative protocol specification was particularly good news, as it meant that there would be just one industrywide IETF specification for a layer 2 tunneling and VPN dial-up protocol.

Similar to the L2F protocol and PPTP, the L2TP facilitates the tunneling of encapsulated PPP frames across an intervening network in a way that is as transparent as possible to both end users and applications. Contrary to the other protocols, however, L2TP uses and even requires the use of IPsec security associations (SAs) to cryptographically protect data that are transmitted between LACs and LNSs. IPsec and IPsec SAs are further addressed in Chapter 14.

After this initial release, the L2TP specification was further refined. In August 1999, a preliminary release was published in RFC 2661 [19] and submitted to the Internet standards track. As such, the L2TP is likely to replace both the L2F protocol and PPTP in the future (this is equally true for Microsoft and Cisco products).