otocol that can be carried within a PPP packet. IPSec offers a variety of advantages. The chief among those are the following: IPSec is widely supported by the industry including Cisco, Microsoft, Nortel Networks, and SO on. This universal presence ensures interoperability and availability of secure solutions for different types and kinds of end users. In addition, all IPSec-compliant products from different vendors are required to be compatible. IPSec provides for transparent security, irrespective of the applications used. IPSec is not limited to operating system-specific solutions, for example. It will be ubiquitous with IP. It will also be a mandatory part of the forthcoming IPv6 standard. IPSec offers a variety of strong encryption standards. The key design decision to support an open architecture provides easy adaptability of newer, stronger cryptographic algorithms. IPSec includes a secure key management solution with digital certificate support. IPSec guarantees the ease of management and use. This reduces deployment costs in large-scale corporate networks. IPSec used in conjunction with L2TP provides secure remote access client-to-server communication. L2TP alone cannot provide for a totally secure communication channel due to its failure to provide per- packet integrity, its incapability to encrypt the user datagram, and the limited security coverage only at the ends of the established tunnel. The major drawback to packet-filtering techniques is that they require access to clear text, both in packet headers and in the packet payloads. When encryption is applied, some or all of the information needed by the packet filters may no longer be available. For example, in transport mode, ESP will encrypt the payload of the IP datagram. In tunnel mode, ESP will encrypt the entire original datagram, both header and payload. In most IPSec-based VPNs, packet filtering will no longer be the princi- ple method for enforcing access control. IPSec's AH protocol, which is cryp- tographic robust, fills that role, thereby