Subject: [Ips] Doubt in Login sequence.

From: Aravind Rajagopal <[email-masked]>
Date: Wed, 11 Jan 2006 10:47:48 +0530

Hi iSCSI Authors,

I'm facing a scenario in the Login Sequence which might be illegal, but I am
unsure of the same. I would like to know what you think of the exchange.

The AuthMethod negotiated is CHAP and once the Chap Challenge is sent by the
Target, the Init responds with the Chap response with CSG=NSG=0 and T=0.
This is validated by the target which finds Authentication to be successful
and the Login Response also has CSG=NSG=T=0.
Now, the Init sends a Login Req with CSG=NSG=0 and T=0 and with no data
attached. The target responds with a Login reponse with Status Class =0x3
indicating failure on the Target side to continue the login.
My concern is over the Last Login Req which according to the draft is not
strictly speaking illegal. So should the target respond with a Login Resp
with again CSG=NSG=T=0. Or is it justified in reporting an error?

Thanks!
Aravind.
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---

From: William Studenmund <[email-masked]>
Date: Wed, 11 Jan 2006 16:45:51 -0800

On Jan 10, 2006, at 9:17 PM, Aravind Rajagopal wrote:

> Hi iSCSI Authors,
>
>  I'm facing a scenario in the Login Sequence which might be illegal, 
> but I am unsure of the same. I would like to know what you think of 
> the exchange.
>
>  The AuthMethod negotiated is CHAP and once the Chap Challenge is sent 
> by the Target, the Init responds with the Chap response with CSG=NSG=0 
> and T=0. This is validated by the target which finds Authentication to 
> be successful and the Login Response also has CSG=NSG=T=0.
>  Now, the Init sends a Login Req with CSG=NSG=0 and T=0 and with no 
> data attached. The target responds with a Login reponse with Status 
> Class =0x3 indicating failure on the Target side to continue the 
> login.
>  My concern is over the Last Login Req which according to the draft is 
> not strictly speaking illegal. So should the target respond with a 
> Login Resp with again CSG=NSG=T=0. Or is it justified in reporting an 
> error?

The target is ALWAYS free to report a Status Class =0x3 error. It can 
do so due to an internal error, because it thinks you won the lottery, 
because it thinks you didn't win the lottery, or because of the phase 
of the moon.

Obviously it is best if it actually logs you in instead, but it is 
permissible.

To be honest, I wonder why the initiator sent the empty NSG=0/T=0 
packet. The only reason to not continue CHAP is if the initiator wants 
to perform mutual auth, but to do so it should have sent a new 
challenge and I value when it sent back the response and name. Thus 
there really is no reason to not be transitioning out of security. So 
the target is probably shutting things down as the initiator looks 
broken.

Take care,

Bill