nologies. With intranets everywhere, IP will be the main corporate network protocol, enhanced to provide end-to-end security, confidentiality, authentication, and integrity over a shared VPN network. The Password Authentication Procedure (PAP) and the Challenge Hand- shake Authentication Protocol (CHAP) do little for security. In fact, PAP and CHAP are part of the basic Point-to-Point Protocol (PPP) suite and fall short in providing a true security procedure. These schemes do not address issues of ironclad authentication and integrity or eavesdropping. The PAP and CHAP are rudimentary procedures used to log onto a network, but hackers and crackers can easily defeat both. Layer 2 Tunnel Protocol (L2TP) is another variation of an IP encapsula- tion protocol. Encapsulating an L2TP frame inside a UDP packet creates an L2TP tunnel. This, in turn, is encapsulated inside an IP packet whose source and destination addresses define the tunnel's ends. Because the outer encapsulating protocol is IP, IPSec protocols can be applied to this composite IP packet, thus protecting the data that flows within the L2TP tunnel. The Authentication Header (AH), Encapsulated Security Payload (ESP), and Internet Security Association and Key Management Protocol (ISAKMP) protocols can all be applied in a straightforward way. L2TPs are an excellent way of providing cost-effective remote access, multiprotocol Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hil Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. SGSN-to-GGSN (Gn) and GGSN-to-PDN (Gi) Interface SGSN-to-GGSN (G) and GGSN-to-PDN (G;) Interface transport, and remote Local Area Network (LAN) access. It does not provide cryptographic robust security. Therefore, L2TP should be used in conjunc- tion with IPSec for providing secure remote access. L2TP supports both host-created and ISP-created tunnels. A remote host that implements L2TP should use IPSec to protect any pr