ISCSI: Urgent Flag requirement violates TCP.

["Douglas Otis" <dotis@sanlight.net>]

Julian,

The result indicated within the iSCSI draft on page 14 will require TCP to
be modified for this statement to be true.  By requiring every message to be
marked, a continued transparent update of the pointer will obscure the
urgent pointer by continued coalescence.  This obscuring coalescence will
occur at both the sender and receiver.  Only a state between normal and
urgent is signaled at the receiver and not the actual pointer.  Unless there
is an intent to modify TCP, this scheme offers no benefit even if offending
portions of the urgent proposal is removed.

   The iSCSI protocol uses the urgent bit in the TCP header to delineate
   iSCSI messages. The first byte of every iSCSI message MUST be marked
   "urgent".  The result is the TCP urgent pointer will point to the
   first byte of the iSCSI message in the TCP segment.

This pointer will be skewed by the size of the send buffer (beyond the TCP
segment) and prevent normal use unless again TCP is modified to comply with
stated expectations.  I would advise complete removal of this Urgent flag
requirement if to remain within the WG charter as only a modified TCP could
use this feature in the intended manner.  This intended manner is plainly
spelled out with concerns about BSD vs. RFC 1122 compliance. There is no
benefit from an occasional toggle between normal and urgent mode.  If you
wish to use a datagram or record based protocol, you are advised to review
RFC 2960.

Doug