Encapsulating Security Payload (ESP)

Encapsulating Security Payload (ESP): An Internet Protocol security (IPSec) protocol that provides confidentiality, in addition to authentication, integrity, and anti-replay. ESP can be used alone, in combination with Authentication Header (AH), or nested with the Layer Two Tunneling Protocol (L2TP). ESP does not normally sign the entire packet unless it is being tunneled. Ordinarily, just the data payload is protected, not the IP header.