This document specifies the details of the Host Identity Protocol
(HIP). HIP allows consenting hosts to securely establish and
maintain shared IP-layer state, allowing separation of the identifier
and locator roles of IP addresses, thereby enabling continuity of
communications across IP address changes. HIP is based on a
Diffie-Hellman key exchange, using public key identifiers from a new
Host Identity namespace for mutual peer authentication. The protocol
is designed to be resistant to denial-of-service (DoS) and
man-in-the-middle (MitM) attacks. When used together with another
suitable security protocol, such as the Encapsulating Security
Payload (ESP), it provides integrity protection and optional
encryption for upper-layer protocols, such as TCP and UDP.
This document obsoletes RFC 5201 and addresses the concerns raised by
the IESG, particularly that of crypto agility. It also incorporates
lessons learned from the implementations of RFC 5201.