Internet Protocol Security

Several projects currently provide development and implementation of IPsec tools. The original IPsec tools are provided by the KAME project, Current versions can be obtained from RPM packages can be obtained from Other IPsec tool projects include the Free Secure/Wide Area Network project (FreeS/WAN) at, which provides a Linux implementation of IPsec tools, and VPN Consortium (VPNC) at, which supports Windows and Macintosh versions. FreeS/WAN provides both Red Hat RPM packages and source code for their tools.

IPsec is made up of several protocols that provide authentication (AH), encryption (ESP), and the secure exchange of encryption keys (IKE). The Authentication Header protocol (AH) confirms that the packet was sent by the sender, and not by someone else. IPsec also includes an integrity check to detect any tampering in transit. Packets are encrypted using the Encapsulating Security Payload (ESP). Encryption and decryption are performed using secret keys shared by the sender and the receiver. These keys are themselves transmitted using the Internet Key Exchange protocol, which provides a secure exchange. ESP encryption can degrade certain compression transmission methods like PPP for dialup Internet connections. To accommodate these compression methods, IPsec provides the IP Payload Compression Protocol (IPComp), with which packets can be compressed before being sent.
The AH, ESP, and IPComp protocols are incorporated into the Linux kernel. The IKE protocol is implemented as a separate daemon. It simply provides a way to share secret keys, and can be replaced by other sharing methods.