This chapter showed you the basics of L2TP and PPTP VPNs. Both have their roots in Microsoft's VPN initiative. PPTP was Microsoft's first VPN implementation, and mostly was an enhanced version of PPP. However, PPTP lacked many security features and thus was combined with the Cisco L2F into L2TP.
Because L2TP doesn't provide for security services such as confidentiality and packet authentication and validation, IPsec is used as a transport. I'll discuss more about how to implement L2TP/IPsec and PPTP remote access VPNs in Chapter 8, "Concentrator Remote Access Connections with PPTP, L2TP, and WebVPN" and Chapter 13, "Windows VPN Client."
Next up is Chapter 5, "SSL VPNs," in which I discuss SSL and its use in implementing VPNs.