As the originator of this thread (sorry), I thought I'd clear up some of
the speculation as to what I'm trying to do. :-)
Our adapter card is a GSN adapter, focused on the ST protocol over a
hippi-6400 link. We support IP on this adapter as well but that's not
its expected primary use. In asking the original question, I was trying
to find out how to disable the IP/TCP software checksums and rely on the
link layer LCRC and ECRC (I think that's what they're called) checks.
The LCRC is a hop to hop CRC that is applied to each 32 byte micropacket
that is transmitted. The ECRC is an overll message CRC that covers all
micropackets of the message. It is my expectation that these two CRCs
will be adaquate to catch any errors that occur within the GSN network.
Note that our card has no IP specific checksum support (it does for
ST) so for packets originating from, or destined to, outside of the
GSN network we _must_ do the software checksuming. I understand this.
My purpose in being able to turn software checksums off was strictly
to measure the performance advantage of doing so. In any real network
environment the software checksums are required with this card.
Thanks,
Bob
On Wed, Jun 06, 2001 at 05:15:40PM -0300, Daniel C. Sobral wrote:
> Louis A. Mamakos wrote:
>
> >
> > If I'm not mistaken the message that started this thread inquired
> > about adding an option to prevent TCP from doing a checksum, since
> > the fancy gigabit hardware performed reliable link-level error detection
>
>
> I do not recall he ever mentioning "link-level". Either my mind removed
> it, or yours inserted it. :-)
>
>
> > itself. I argue that since TCP is an end-to-end transport protocol that
> > individual error detection on a per-hop basis is not sufficient either
> > theoretically or practically. My last message illustrated a number of
> > cases where the transport of the packet over a link was reliably
> > done, but the contents of the packet were corrupted by malfunctioning
> > software or hardware which the end-to-end TCP checksum detected.
> >
> > I have less of an issue with the endpoints of the TCP connection
> > offloading checksum computation to the NIC card, though you're
> > still exposed to a certain class of error, like the PR I referenced.
> > The problem is what happend to your data in intermediate network
> > elements (routers, etc.) between the endpoints of the TCP connection.
> >
> > Louis Mamakos
> >
> >
> > To Unsubscribe: send mail to [EMAIL PROTECTED]
> > with "unsubscribe freebsd-hackers" in the body of the message
> >
>
>
> --
> Daniel C. Sobral (8-DCS)
> [EMAIL PROTECTED]
> [EMAIL PROTECTED]
> [EMAIL PROTECTED]
> [EMAIL PROTECTED]
>
> ... if the church put in half the time on covetousness that it does
> on lust, this would be a better world.
> -- Garrison Keillor, "Lake Wobegon Days"
--
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