Re: Urgent as Framing Hint?

["David P. Reed" <dpreed@reed.com>]

At 06:19 PM 12/1/00 +0100, Luigi Rizzo wrote:

>not that i don't like the idea, but this way any "standard" receiver
>will not understand the new checksum and drop the packet. Net effect
>is that you can only talk to systems that understand the new checksum
>style unless you have some way to negotiate thhis feature.

One way to negotiate this feature is to use it and see what happens.  The 
basic approach would be to send a datagram containing the variant checksum 
as the first datagram in the TCP stream.  If the receiver discards the 
frame, it will never acknowledge it, even upon retries.  If it receives an 
acknowledgement, also variant-marked, the sender and receiver conclude the 
negotiation.  If not, the sender can then drop the connection and indicate 
to the TCP client that the variant-marking of frames is not supported, and 
a default could be used.

>If you
>don't, i fail to see how this is different from having a totally
>different protocol which happens to have the same ID as TCP (perhaps
>to get through firewalls ?).

Well, TCP-Reno is  by this definition a "different protocol which happens 
to have the same ID as TCP", right?

Please be aware, I make this suggestion because the idea seems to be 
helpful and low cost, given the constraints that the iSCSI folks seem to be 
laboring under.  I leave advocacy and discussion of the impacts to others, 
esp. those whose needs benefit and those who know of adverse impacts.  But 
I hope it might be a way out of a heated conflict where all sides have some 
legitimate concerns.



- David
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