Thanks Yoav.

If responder chooses to decline it, then does it force the fallback on tunnel 
mode? I am asking this because sometime back I had a doubt regarding the 
following lines in RFC 5996.

 " If  responder declines the request, the Child SA will be established in

   tunnel mode.  If this is unacceptable to the initiator, the initiator

   MUST delete the SA."


It seemed to me that this was implementation's choice to establish the SA in 
tunnel mode or send "NO_PROPOSAL_CHOSEN" in this case.


--

Regards,

Hema


From: Yoav Nir <[email protected]<mailto:[email protected]>>
Date: Thursday, 12 November 2015 12:47 pm
To: Hema Tripathi <[email protected]<mailto:[email protected]>>
Cc: "[email protected]<mailto:[email protected]>" 
<[email protected]<mailto:[email protected]>>
Subject: Re: [IPsec] Clarification regarding USE_TRANSPORT_MODE notification

Hi, Hema

USE_TRANSPORT_MODE is a notification, so it is outside the structures in the SA 
payload.

As a consequence, the protocol does not allow you to propose AES-GCM in 
transport mode or ChaCha20/Poly1305 in tunnel mode.

Note also that USE_TRANSPORT_MODE does not force transport mode. It only shows 
support. The responder can then choose to include it (agreeing to use transport 
mode) or not (forcing you back to tunnel).

And yes, notifications were not supposed to be used for negotiations.

HTH,

Yoav

On 12 Nov 2015, at 8:59 AM, Hema Tripathi (hetripat) 
<[email protected]<mailto:[email protected]>> wrote:

Hi,

I have a doubt regarding USE_TRANSPORT_MODE in IKEv2. Does this apply to 
complete SA offer(s) or to each proposal in the SA? In case of multiple 
proposals, should they be negotiated on the basis of the mode configured for 
that proposal? Or should all SA offers adhere to same mode?

-
Regards,
Hema
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