ESP
acronymnetworkingsecurity
Stands for: Encapsulating Security Payload
The IPsec protocol that encrypts and authenticates packet payloads.
Encapsulating Security Payload (RFC 4303) is the IPsec component that provides confidentiality and integrity for tunneled traffic. A capture taken outside the tunnel sees only ESP, not the protected inner packets.
Encapsulating Security Payload is the IPsec protocol that actually protects traffic, providing confidentiality, integrity and authentication. It is IP protocol 50, not a UDP or TCP port, which is the fact that explains most of its operational difficulty.
Because it has no ports, address translation cannot rewrite it and stateful firewalls often cannot track it, which is why NAT traversal encapsulates it in UDP. Tunnel mode protects the entire original packet and is what site-to-site VPNs use; transport mode protects only the payload and is used between hosts. Its sibling AH provides integrity without encryption and is essentially unused, because integrity without confidentiality is rarely what anyone wants.
Also known as: esp