[strongSwan] IKEv1 - Message-IDs during phase 1 for encrypted Notify messages

[Владимир Подобаев]

Hello!

I want to ask IKEv1 experts.
Suppose during phase 1 - key exchange went ok. Suppose - a notification message is sent on some reason (during phase 1).
It is encrypted (because key exchange completed). 

A question: What Message ID will the Notify message have? Zero or unique non-zero? I can't figure it out from RFCs.

Great thanks in advance!

Best regards, Vladimir Podobaev