"This document specifies how to use the Internet Key Exchange (IKE) protocols@ such as IKEv1 and IKEv2@ to setup ""unauthenticated"" security associations (SAs) for use with the IPsec Encapsulating Security Payload (ESP) and the IPsec Authentication Header (AH). No changes to IKEv2 bits-on-the-wire are required@ but Peer Authorization Database (PAD) and Security Policy Database (SPD) extensions are specified. Unauthenticated IPsec is herein referred to by its popular acronym@ ""BTNS"" (Better-Than-Nothing Security)."
RFC 5386-2008 history
2008RFC 5386-2008 Better-Than-Nothing Security: An Unauthenticated Mode of IPsec