Internet Protocol security defined
Internet Protocol security (IPSec) is a framework of open standards for ensuring private, secure communications over Internet Protocol (IP) networks, through the use of cryptographic security services. The Microsoft Windows XP implementation of IPSec is based on standards developed by the Internet Engineering Task Force (IETF) IPSec working group.
IPSec is the long-term direction for secure networking. It provides aggressive protection against private network and Internet attacks through end-to-end security. The only computers that must know about IPSec protection are the sender and receiver in the communication. In Windows XP, IPSec provides the ability to protect communication between workgroups, local area network computers, domain clients and servers, branch offices (which might be physically remote), extranets, and roving clients.