RE: iSCSI: DLB's [T.6] 2.3 iSCSI Session Types

[Black_David@emc.com]

Ayman,

> The issue that came up before was if a discovery session could be kept
open,
> why not allow the initiator and target to send NOPs, and allow the target
to
> send Async messages when new targets become available?
> 
> I don't mean to bring up this issue again at this stage, but using "MAY"
> leaves room for implementations that want to support this. If we allow NOP
> and Async PDUs on a discovery session, then changing "MAY" to "MUST" will
be
> fine.

That would be fine with me as long as we spell out which Async PDUs are used
and what they do - it looks like codes 1 (target requests logout), 3 (target
is closing session) and 4 (target requests negotiation) would be acceptable,
with code 4 having the meaning "please issue a Send Targets" when used on a
discovery session.  The text to specify this needs to be more than just the
single "MUST" in order to avoid applying a "MUST" to long-lived discovery
session support.  Here's an attempt, but it's a bit long and could use
some editing:

On a discovery session, an Initiator:
- MUST NOT issue PDUs other than Send Targets, a logout request to close
	the session, and NOP-Out.
- MAY ignore NOP-In and Async Message PDUs from the target, but MUST NOT
	treat NOP-In and Async Message PDUs with codes 1, 3, and 4 as
errors.
	(Hmm ... ignoring code 1 [request logout] and 3 [target is closing
	session] does not seem like a good idea, although it does work as
	the target can time-out and tear down the session itself).
- MUST treat an Async Message PDU with code 4 (negotiation request) as a
	request to issue a Send Targets command, although the initiator MAY
	ignore the request.
- MUST treat as a protocol error (terminate session), any
	received PDU other than (1) NOP-In, (2) Async Message and (3)
	responses to PDUs issued by the Initiator.

On a discovery session, a Target:
- MUST accept and respond to Send Targets and a logout request to
	close the session.
- MAY ignore NOP-Out PDUs from the initiator, but MUST NOT treat them as
	errors.
- MUST NOT issue PDUs other than NOP-In, Async Message PDUs with codes 1
	(request logout), 3 (announce session closure) and 4 (request
	negotiation), and PDUs required to respond to Send Targets and
	a logout request from the Initiator.
- MUST treat as a protocol error (terminate session), any
	received PDU other than (1) a text PDU containing Send Targets,
	(2) a Logout Request to close the session, and (3) NOP-Out.

My underlying motivation is that if we're going to allow long-lived
discovery sessions, it behooves us to specify how they work sufficiently
for interoperability.

Thanks,
--David
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David L. Black, Senior Technologist
EMC Corporation, 42 South St., Hopkinton, MA  01748
+1 (508) 249-6449            FAX: +1 (508) 497-8018
black_david@emc.com       Mobile: +1 (978) 394-7754
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