I don't think we should really prohibit such extensions and enhancements.  It's 
just that IKE will fail if you try it with a peer that does not support it.

As far as the end-user is concerned, this is not different from an 
UNSUPPORTED_CRITICAL_PAYLOAD in IKE_AUTH.  Either way, the tunnel setup fails.

Do you see any cause for concern in the UNSUPPORTED_CRITICAL_PAYLOAD being sent 
in a non-encrypted unauthenticated message?  Or in a response to such?

________________________________
From: [email protected] [mailto:[email protected]] On Behalf Of Yaron 
Sheffer
Sent: Monday, April 27, 2009 10:52 PM
To: IPsecme WG
Subject: [IPsec] Issue #37: UNSUPPORTED_CRITICAL_ERROR during initial IKE_INIT

>  2.5.  Version Numbers and Forward Compatibility
...
>     IKEv2 adds a 'critical' flag to each payload header for further
>     flexibility for forward compatibility.  If the critical flag is set
>     and the payload type is unrecognized, the message MUST be rejected
>     and the response to the IKE request containing that payload MUST
>     include a Notify payload UNSUPPORTED_CRITICAL_PAYLOAD, indicating an
>     unsupported critical payload was included. {{ 3.10.1-1 }} In that
>     Notify payload, the notification data contains the one-octet payload
>     type.  If the critical flag is not set and the payload type is
>     unsupported, that payload MUST be ignored.  Payloads sent in IKE
>     response messages MUST NOT have the critical flag set.  Note that the
>     critical flag applies only to the payload type, not the contents.  If
>     the payload type is recognized, but the payload contains something
>     which is not (such as an unknown transform inside an SA payload, or
>     an unknown Notify Message Type inside a Notify payload), the critical
>     flag is ignored.

Tero:

What if such UNSUPPORTED_CRITICAL_PAYLOAD error happens during the
initial IKE_SA_INIT message, or do we forbid enhancements and
modifications which might cause such error?

Paul: Not done. This is interesting, but should be discussed on the list.



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