IP Security Protocol, or IPsec, refers to a suite of protocols that provide security for Internet Protocol (IP) network communications through the use of cryptography. It can establish host authentication at the start of a communication session, and it negotiates cryptographic keys that will be used during the course the communication. IPsec is able to secure data transmission between two hosts, two security gateways, as well as a host and a security gateway. Since it functions at the Internet layer of the IP suite, it can provide security for all classifications of Internet application traffic.

Here are some websites that provide more information about IPsec: