Subject: RE: [Ips] Discovery text

From: [email-masked]
Date: Mon, 19 Sep 2005 12:00:43 -0400

> It would seem to me that since there may be a requirement to 
> change existing code to comply with this you should increase
> the version number.

That's not going to happen, but something does need to be done
about negotiation to avoid breaking things ...

  5.1	Error Recovery for Discovery Sessions

  The negotiation of the key ErrorRecoveryLevel is irrelevant for 
  Discovery sessions - i.e. for sessions that negotiated 
  "SessionType=Discovery".  The operational ErrorRecoveryLevel for 
  Discovery sessions MUST be 0.  This naturally follows from the 
  functionality constraints [RFC3720] imposes on Discovery sessions.

As written, this allows an ErrorRecoveryLevel=Irrelevant response
on a discovery session, which may cause problems for an implementation
that is not expecting such a response.  The text needs to instead
- Note/warn that older implementations may attempt to use non-zero
	ERL on a discovery session, and it is therefore not an error
	to receive such an attempt,
- But if ERL is negotiated on a discovery session, it MUST be
	offered and responded to as zero.
Older implementations would escape the second bullet's "MUST" by
not claiming compliance to the implementers guide RFC.  Fortunately,
ERL negotiation has a "minimum" result function, so one side can
force it to zero without the other's cooperation.

For the ISID rule clarifications, we need to make sure that an
implementation respecting the new rules does something reasonable
at ERL 0 when talking to a system that has not complied with
the clarifications.

Thanks,
--David
----------------------------------------------------
David L. Black, Senior Technologist
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953             FAX: +1 (508) 293-7786
[email-masked]        Mobile: +1 (978) 394-7754
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From: "Mallikarjun C." <[email-masked]>
Date: Mon, 19 Sep 2005 14:52:18 -0700

> on a discovery session

That wasn't what I intended (didn't use the capitalized Irrelevant), but 
I can now see how that can be read into what I wrote.

 >The text needs to instead

OK, I will incorporate the suggestions.

 > at ERL 0

I am not certain that the new UNNAMED ISID RULE interacts with error 
recovery or its negotiation.  Please let me know if you see it otherwise.

Thanks!

Mallikarjun

Mallikarjun Chadalapaka
Networked Storage Architecture
StorageWorks Division
Hewlett-Packard MS 5668
Roseville CA 95747
cbm [at] rose.hp.com

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From: William Studenmund <[email-masked]>
Date: Mon, 19 Sep 2005 16:04:54 -0700

> at ERL 0 when talking to a system that has not complied with

I think the problem is that things don't work well without the 
clarifications. This particular part of things isn't (AFAICT) one where 
we had one working behavior which we want to replace with another, but 
it is a place where we had a mess we want to clean up. :-)

Take care,

Bill