RFC Errata
RFC 3947, "Negotiation of NAT-Traversal in the IKE", January 2005
Source of RFC: ipsec (sec)
Errata ID: 4936
Status: Reported
Type: Technical
Publication Format(s) : TEXT
Reported By: Nikolai Malykh
Date Reported: 2017-02-16
Section 5.2 says:
The NAT-OA payloads are sent inside the first and second packets of Quick Mode. The initiator MUST send the payloads if it proposes any UDP-Encapsulated-Transport mode, and the responder MUST send the payload only if it selected UDP-Encapsulated-Transport mode. It is possible that the initiator sends the NAT-OA payload but proposes both UDP-Encapsulated transport and tunnel mode. Then the responder selects the UDP-Encapsulated tunnel mode and does not send the NAT-OA payload back.
It should say:
The NAT-OA payloads are sent inside the first and second packets of Quick Mode. The initiator MUST send the payloads if it proposes any UDP-Encapsulated mode, and the responder MUST send the payload only if it selected UDP-Encapsulated-Transport mode. It is possible that the initiator sends the NAT-OA payload but proposes both UDP-Encapsulated transport and tunnel mode. Then the responder selects the UDP-Encapsulated tunnel mode and does not send the NAT-OA payload back.