L2TP: Implementation and Operation

With its inherent support for the IPSec specifications, Layer 2 Transport Protocol (L2TP) has become a powerful tool for developers of Virtual Private Networks (VPNs). It allows for secure transmissions over an open network, and, unlike Point-to-Point Tunneling Protocol (PPTP), allows for connections to the Internet by both SLIP and PPP links. L2TP: Implementation and Operation shines a bright light on this flexible tunneling protocol that traces its lineage to both PPTP and Cisco's Layer 2 Forwarding (L2F) protocol.

The book is more than adequate as an academic and strategic overview of L2TP technologies for people thinking about deploying them on a VPN. It's also a valuable resource for programmers planning to implement L2TP in their software.

VPN administrators will appreciate author Richard Shea's presentations on various architectures for VPNs running L2TP. Presented both as clip-art diagrams that illustrate relationships among machines and as schematics that show the relationships among various protocols, the network-design material is thorough. So is Shea's dissection of the protocol--he picks each kind of L2TP message apart, explaining what the control messages say and how the data messages present their contents. With byte listings and state diagrams, he tells programmers what they need to know about L2TP behavior under various circumstances. You might want to back this book with the IPSec coverage in IPSec. --David Wall

Topics covered: Strategic advantages of L2TP, strategies for implementing L2TP on VPNs, L2TP states and transitions, control channels, session management, and security.