PPP and L2TP: Remote Access Communications

Security may be the single biggest impediment to the truly distributed workforce, in which telecommuters and remote consultants can collaborate on equal terms with those on a local area network (LAN). Virtual private networks (VPNs), underpinned by robust and secure PPP and L2TP connections, are emerging as a solution. In PPP and L2TP: Remote Access Communications, Uyless Black (perhaps best known for his Voice Over IP), explains both connectivity solutions in terms that are a bit academic but clearly less so than the raw protocol specifications to which he makes frequent reference. You'll appreciate his approach if you're a step removed from the technicalities of L2TP and PPP (perhaps as a salesperson or manager), or if you're a network programmer looking for an introduction that will allow you to approach further research intelligently.

The most valuable parts of Black's book are those in which he describes the "conversations" that occur between network nodes. Using lots of prose and plenty of state diagrams, flow charts, and packet diagrams, the author makes it clear which node sends what signals, when and why, and how those signals affect the condition of the system as a whole. Though Black's explanations are in depth, you may want to supplement this book with others that provide more details about specific remote connectivity technologies. PPP Design and Debugging is the definitive work on its subject, while L2TP: Implementation and Operation has a lot of useful things to say about that emerging standard. IP Sec is worth studying too. --David Wall

Topics covered: PPP, Layer 2 Tunneling Protocol (L2TP), and their applications to distributed networking; explores the signals that make up the data link layer in depth to show how PPP establishes and controls connections with its Link Control Protocol (LCP) and Network Control Protocol (NCP); PPP security and Multilink Protocol (MP); and L2TP coverage includes information on the protocol's relationships with the IP Secure standard and physical networks of various kinds (including frame relay and Mobile PPP).