IPSec—IPSec is used for communication among two or more hosts, two or more subnets, or hosts and subnets. This IP network layer packet security protocol establishes VPNs via transport and tunnel mode encryption methods. For the transport method, the data portion of each packet—referred to as the encapsulation security payload (ESP)—is encrypted to achieve confidentiality. In the tunnel mode, the ESP payload and its header are encrypted. To achieve nonrepudiation, an additional authentication header (AH) is applied.