Re: Status summary on multiple connections

["Randall R. Stewart" <randall@stewart.chicago.il.us>]

"Mark A. Carlson" wrote:
> 
> "Randall R. Stewart" wrote:
> >
> > I really do NOT see how one can allow a TCP to deliver out of order
> > though, oh
> > I know technically how to do it, but it is a fundamental violation
> > of what TCP is supposed to be delivering.... i.e. the bytes being
> > transfered from 0 to N...
> 
> The scenario which everyone seems to be worried about is that
> packets are delivered in order, but the ACK for one of them is
> lost going back. Everything gets delivered to iSCSI, then the
> non-ACKed packet is delivered again.
> 
> Does this really happen in today's stacks?
> 
Well, a transport stack must ALWAYS be prepared for
duplicates...

However.. has you state below.. if the above happens TCP
will recognize it IS a duplicate and drop the duplicate..

The upper layer (iSCSI in this case) will NEVER see the
duplicate data... If it DOES see duplicate data then you
have a BROKEN TCP stack...

R


> It seems like the TCP stack would see it as a duplicate that
> has already been delivered to the upper layer and drop it.
> TCP does have sequence numbers and knows this. The only way
> I could imagine this happening is if there was sufficient
> data to wrap the TCP sequence space.
> 
> -- mark

-- 
Randall R. Stewart
randall@stewart.chicago.il.us or rrs@cisco.com
815-342-5222 (cell) 815-477-2127 (work)