Re: ISCSI: Urgent Flag requirement violates TCP.

["Venkat Rangan" <venkat@rhapsodynetworks.com>]

I am sure this was considered and rejected, but I'm unable to locate a
previous memo/email, in this long thread, where this has been rejected. I
apologize if this is reopening something that was already settled.

Is there an alternative to the Urgent Pointer mechanism for framing, where
TCP implementations can negotiate whether or not they ensure iSCSI header to
be immediately following the TCP header. While generic TCP stacks may not
have a notion of higher level protocol framing, what are the downsides to
two iSCSI peers (and their modified TCP stacks) negotiating this? Each iSCSI
PDU is limited to the size of a TCP MSS, and that the sender indicates to
the receiver (at login) that it guarantees that iSCSI header always follows
TCP header. If a particular sender doesn't indicate this, the TOE can still
work in a memory-constrained mode. This may cause some TCP segments to be
short of the agreed-upon MSS (wire usage inefficiency), but is this a
significant loss?

Does the WG operating requirement of "MUST work with existing TCP/IP stacks"
prevent this?

As long as there are no other intermediate entities terminating the TCP
connection (such as a Layer 4 load balancer), the TCP segment at the
receiving end would appear in-tact. If a header alignment violation is found
(parse error on iSCSI header), the receiver can revert to the memory
constrained mode.

Regards,

Venkat Rangan
Rhapsody Networks Inc.
www.rhapsodynetworks.com