IKEv2 specifies that Extensible Authentication Protocol (EAP) authentication must be used together with responder authentication based on public key signatures. This is necessary with old EAP methods that provide only unilateral authentication using@ e.g.@ onetime passwords or token cards. This document specifies how EAP methods that provide mutual authentication and key agreement can be used to provide extensible responder authentication for IKEv2 based on methods other than public key signatures.