Short for
Encapsulating Security Payload, the ESP
header is designed to provide a mix of security services in
IPv4 and IPv6. ESP may be applied alone, in
combination with the IP
Authentication Header
(AH), or in a nested fashion. The ESP header is inserted after the IP
header and before the upper layer protocol header
(transport
mode) or before an encapsulated IP header
(tunnel mode). ESP is used to provide confidentiality, data origin
authentication, connectionless integrity, an
anti-replay service, and limited traffic flow confidentiality.
[Adapted
from (RFC2406)]
