RE: ISCSI: More on Urgent pointer

[Silvano Gai <sgai@cisco.com>]

At 09:00 AM 11/14/2000 -0500, Black_David@emc.com wrote:
>With my WG co-chair hat firmly on ...
>
>> There are two cases here.  One where the iSCSI proposal is repaired to
>> reflect normal operation of TCP and another case where the present
>proposal
>> stands as written.  As written, there is an expectation of there being a
>> record mark for every TCP segment that contains the beginning of the first
>> PDU
>
>... let me make it completely clear that the WG must pursue the first
>case.  We do not have license to make changes to RFC 793, and iSCSI
>MUST be capable of working with unmodified host TCP stacks.  These
>matters are not open to discussion; send me email directly with questions
>and clarifications.  I note that about a week ago I indicated that the
>text Doug is objecting to is incorrect and has to be modified.
>
>I also believe that based on discussion on the list, WG rough consensus
>does NOT exist for requiring this use of the URG flag and Urgent pointer,
>(too many people have objected to making them mandatory), and hence
>the current "MUST" will have to be replaced.  Off the list, someone has
>also pointed out that setting the URG flag is likely to break header
>prediction in some existing host TCP stacks.  Further discussion on
>whether this ought to be a "SHOULD" or a "MAY" is welcome, 

David,

I don't think that changing MUST to SHOULD or MAY is going to solve the problem. If the two ends do not agree whether using or not the Urgent Pointer, you may end up in a very unoptimized situation.

For Example:
- Server S has iSCSI in HW and supports UP (Urgent Pointer)
- Client C has iSCSI in SW (e.g. a laptop)

When S sends to C, C fails the "header prediction test" and goes to the slow path, since UP is present.

I don't think we want to implement UP negotiation. Correct?

Cheers

-- Silvano



Silvano Gai               
Cisco Systems                  Empowering the Internet Generation
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