Re: iSCSI : Reject PDU Concerns.

[Matt Wakeley <matt_wakeley@agilent.com>]

I disagree with you Doug,

Douglas Otis wrote:
> 
> Matt,
> 
> Unless encoding headers to hide typical PDU signatures, an analyzer will
> have little difficulty in discovering PDU boundaries.

I think that at 10Gig, it will be very difficult for an analyzer to find an
iSCSI header in a byte stream and keep up with the incoming traffic while it's
doing it. Furthermore, I could come up with a data pattern that would make it
really difficult for your searching analyzer to synchronize on the real PDUs
vs the fake ones in the data.

> Should a scheme force
> PDU alignment every 8192 bytes as example, discovery would be a certainty
> within 8k bytes.

How is that?  Remember, TCP's initial sequence number is random, so how will
you know where the 8K boundary is?

> To prevent blockage, the size of the PDU is limited and so
> the search is not impossible as you imply nor even difficult.  Either
> markers or alignment seems a good solution for minimizing impact of segment
> loss to that of the interval rather than 2RTT x rate.  For either a periodic
> marker or alignment scheme to work for sending, no changes to TCP is
> required.

Tweeking TCP a little by adding even an option bit in the header signalling a
start of a new PDU would be a lot better.  TCP and any other protocol should
evolve to track the evolution of the rest of computer technology.

-Matt