Red Hat Enterprise Linux supports IPsec for connecting remote hosts and networks to each other using a secure tunnel on a common carrier network such as the Internet. IPsec can be implemented using a host-to-host (one computer workstation to another) or network-to-network (one LAN/WAN to another). The IPsec implementation in Red Hat Enterprise Linux uses Internet Key Exchange (IKE), which is a protocol implemented by the Internet Engineering Task Force (IETF) to be used for mutual authentication and secure associations between connecting systems.
An IPsec connection is split into two logical phases. In phase 1, an IPsec node initializes the connection with the remote node or network. The remote node/network checks the requesting node's credentials and both parties negotiate the authentication method for the connection. On Red Hat Enterprise Linux systems, an IPsec connection uses the pre-shared key method of IPsec node authentication. In a pre-shared key IPsec connection, both hosts must use the same key in order to move to the second phase of the IPsec connection.
Phase 2 of the IPsec connection is where the security association (SA) is created between IPsec nodes. This phase establishes an SA database with configuration information, such as the encryption method, secret session key exchange parameters, and more. This phase manages the actual IPsec connection between remote nodes and networks.
The Red Hat Enterprise Linux implementation of IPsec uses IKE for sharing keys between hosts across the Internet. The racoon keying daemon handles the IKE key distribution and exchange.