Re: [storm] iSCSI version descriptors

<david.black@emc.com> Tue, 08 March 2011 16:21 UTC

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From: <david.black@emc.com>
To: <cbm@chadalapaka.com>, <storm@ietf.org>
Date: Tue, 8 Mar 2011 11:22:05 -0500
Thread-Topic: [storm] iSCSI version descriptors
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Subject: Re: [storm] iSCSI version descriptors
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Mallikarjun,

While I think your option 1) is ok:

> 1) When a feature is completely obsoleted (e.g. markers) relative to 3720,
> iSCSI consolidated spec requires that the corresponding keys be negotiated
> to "No" (e.g. OFMarker=No).

My design preference is to recommend (SHOULD) a "Reject" value response, which is allowed by RFC 3720 and has the additional virtue of carrying a "What on earth do you think you're doing?" implication back to the clue-impaired implementation that tried to use the obsolete feature.  In any case, we're in clear agreement that a "NotUnderstood" response has to be prohibited.

> 2) When a feature *option* is obsoleted (e.g. SPKM1 & SPKM2 for AuthMethod),
> the spec does nothing special.    The existing iSCSI negotiation semantics
> are comprehensive enough that two spec-compliant implementations will
> negotiate to the correct result because the obsoleted options for that
> feature are not offered as negotiables.

That covers half the cases - new initiator with new or old responder.  With an old initiator, it is possible that obsolete options are offered.  If obsolete options are offered in combination with one or more supported options, everything should work fine.  If obsolete options are the only ones offered, "Reject" is an appropriate response.

Thanks,
--David

> -----Original Message-----
> From: Mallikarjun Chadalapaka [mailto:cbm@chadalapaka.com]
> Sent: Monday, March 07, 2011 5:13 PM
> To: Black, David; storm@ietf.org
> Subject: RE: [storm] iSCSI version descriptors
> 
> David,
> 
> In trying to determine what if any text needs to change in the consolidated
> spec after this discussion, I did a re-reading of this whole thread - up to
> DavidH's most recent note.   I stumbled on the following:
> 
> >  When we take out a feature in the new iSCSI consolidated draft, the easiest
> >  thing to do is allow a NotUnderstood response to the keys that negotiate
> >  that feature.  This should not pose a problem for unimplemented features,
> >  but it would be a behavior change.  The completely backwards-compatible
> >  alternative is have the consolidated iSCSI draft list the keys used for
> >  removed features and prohibit a NotUnderstood response to those keys
> >  (Reject would be an acceptable alternative response).
> 
> I do not believe the consolidated spec needs to change the current
> negotiation semantics.  I suggest a third option:
> 1) When a feature is completely obsoleted (e.g. markers) relative to 3720,
> iSCSI consolidated spec requires that the corresponding keys be negotiated
> to "No" (e.g. OFMarker=No).
> 
> 2) When a feature *option* is obsoleted (e.g. SPKM1 & SPKM2 for AuthMethod),
> the spec does nothing special.    The existing iSCSI negotiation semantics
> are comprehensive enough that two spec-compliant implementations will
> negotiate to the correct result because the obsoleted options for that
> feature are not offered as negotiables.
> 
> 
> This should minimize the core protocol changes, and related impacts to
> existing interop tests.
> 
> Comments are welcome.  With the fast-approaching Prague deadline, I will go
> ahead with the spec'ing this option if I don't hear any disagreement on this
> by this Wednesday.
> 
> Thanks.
> 
> Mallikarjun
> 
> 
> 
> 
>   -----Original Message-----
>   From: storm-bounces@ietf.org [mailto:storm-bounces@ietf.org] On Behalf
>   Of david.black@emc.com
>   Sent: Thursday, October 21, 2010 10:15 PM
>   To: storm@ietf.org
>   Subject: [storm] iSCSI version descriptors
> 
>   One more time on this issue.  This is for discussion - it's not an
>   announcement of a decision.  This is the only real issue that needs to be
>   resolved to complete the new (SAM) features draft for iSCSI.
> 
>   Reminder: we need to define a set of small positive integer values to
>   describe the iSCSI version starting with 0 = "no version claimed".  After
>   some private discussions, it appears that we need two additional version
>   values beyond 0.
> 
>   The first observation is that the baseline should be at least RFC 3720
>   (original iSCSI) + RFC 5048 (Corrections and Clarifications).  That would
> be
>   version value 1.
> 
>   The next observation is that taking features out of the consolidated iSCSI
>   draft may allow a visible behavior change.  RFC 3720 has this to say about
>   text keys for negotiation:
> 
>      All keys in this document, except for the X extension formats, MUST
>      be supported by iSCSI initiators and targets when used as specified
>      here.  If used as specified, these keys MUST NOT be answered with
>      NotUnderstood.
> 
>   When we take out a feature in the new iSCSI consolidated draft, the
> easiest
>   thing to do is allow a NotUnderstood response to the keys that negotiate
>   that feature.  This should not pose a problem for unimplemented features,
>   but it would be a behavior change.  The completely backwards-compatible
>   alternative is have the consolidated iSCSI draft list the keys used for
>   removed features and prohibit  a NotUnderstood response to those keys
>   (Reject would be an acceptable alternative response).
> 
>   If we're careful about this, the same version value can apply to 3720/5048
>   and the consolidated iSCSI draft.  I'd suggest that we be careful, and the
>   details of how can be worked out as we finalize the consolidated draft - I
>   think we should have at least one more round of looking at features to
>   remove.
> 
>   After that, we'll need a version value for the new (SAM) features draft
>   additions.  The result would be 3 version values:
>   	0 = no version claimed
>   	1 = 3720/5048 or new consolidated draft
>   	2 = (3720/5048 or new consolidated draft) + SAM 4/5 features
>   from the SAM draft.
> 
>   Comments?
> 
>   The SAM 4/5 features draft will expire while draft submission is closed
> for
>   the Beijing meeting - if we can resolve this issue, the next version of
> that
>   draft could be submitted shortly after draft submission opens again, and
>   would probably go to WG Last Call shortly thereafter.
> 
>   Thanks,
>   --David
>   ----------------------------------------------------
>   David L. Black, Distinguished Engineer
>   EMC Corporation, 176 South St., Hopkinton, MA  01748
>   +1 (508) 293-7953             FAX: +1 (508) 293-7786
>   david.black@emc.com        Mobile: +1 (978) 394-7754
>   ----------------------------------------------------
> 
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