http://www.rfc-editor.org/rfc/rfc3947.txt
RFC 3947: Negotiation of NAT-Traversal in the IKE, T. Kivinen, B. Swander, A. Huttunen, V. Volpe2005-01-01T23:00:00-00:00This document describes how to detect one or more network address translation devices (NATs) between IPsec hosts, and how to negotiate the use of UDP encapsulation of IPsec packets through NAT boxes in Internet Key Exchange (IKE). [STANDARDS-TRACK]