Re: slow ethernet

[Greg Wooledge <greg@wooledge.org>]

Nick Holland (nick@holland-consulting.net) wrote:

> The problem with extreme statements is they can be disproven with one
> counterexample.  (Henning will deny it was a counter example 8-).

Need more counterexamples?  Take Dr. D_____'s Dell Latitude laptop
which has a built-in 3c905 card (don't know the exact model number).
Plug it into the wall jack (the red one) behind my chair.  It's connected
to some sort of Cisco switch; I don't know which model.  The card will
autonegotiate "10baseT-HD", at least under Linux.  The transfers will
suck rocks, because the switch port is set to 10baseT-FD.  Now, want to
be even more dumbfounded?  Manually set the card to 10baseT-FD using the
Linux "mii-tool" command, and the transfer will *STILL* suck rocks -- at
least, downloading to the laptop.  Uploading from the laptop works great
at that setting.  (Not that this helps much when I'm trying to download
security updates to the laptop....)  Oh, and there are dmesg errors, too.

Take the very same laptop, and the very same cable, and plug it into
the *blue* wall jack behind my chair.  Same switch, different settings;
this one's set to 100baseTX-HD.  The laptop autonegotiates correctly,
and data transfers in both directions are at full speed.

Why is that red port set to 10-FD?  Because our networking department
decided to use that as the new "standard".  We have to request that
individual ports be set to different settings on a per-port basis.
This doesn't help roaming users *at all*.

We have some data acquisition systems which are HP workstations on
wheels.  They have built-in HP network interface cards, and they run
HP-UX 10.20.  They move around from building to building, floor to
floor, so they *have* to be set to autonegotiate.  Whenever any of
these machines is plugged into a port that's set to FULL duplex, it
fails autonegotiation.  Every time.  Manually setting the interface
to HALF duplex (at the same speed) works.  I've written some shell
scripts which run at boot time and attempt to transfer data (the X
server binary) to some other systems over NFS.  If I get a particular
failure message ("Cannot close ...") then I change the duplex, sleep
for 11 seconds, and try again.  This is a *nasty* hack, but it does
seem to work.  It's the only thing that does.

(Oh, and there are also some menu choices that the end users can
use to manually change the duplex/speed settings, through sudo.
Most of the users are afraid to touch those; I don't blame them.)

> Autonegotiation CAN BE problematic for a number of reasons.  You must
> keep it as an option in your trouble shooting toolkit.

It's on the *top* of my toolbox, and it never gets dusty.  Henning's
living in a fantasy land.

I apologize for the long, mostly-off-topic message.  OK, not really. ;-)

--
Greg Wooledge                  |   "Truth belongs to everybody."
greg@wooledge.org              |    - The Red Hot Chili Peppers
http://wooledge.org/~greg/     |

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