funky network slowdown

["N. Thomas" <nthomas@cise.ufl.edu>]

Our network: a DSL modem that feeds into an OpenBSD box that does
firewall/nat; the OpenBSD box feeds into a switch; and the switch is hooked
up to three computers: a Debian, Red Hat, and Windows 2000 box.

Here is roughly what it looks like:

                                       [Debian]
                                     /
    [Internet] - [OpenBSD] - |switch|- [Win2k]
                                     \
                                       [RedHat]

Okay, so I was getting some funky speeds between the Debian and RedHat
boxes, so I tested it. I took a large file transfered it between the
different machines. Here is the result:

    Internet <-> OpenBSD = 64Kbs
    Internet <-> RedHat  = 64Kbs
    Internet <-> Windows = 64Kbs
    Internet <-> Debian  = 64Kbs
    OpenBSD  <-> Windows = 1Mbs
    OpenBSD  <-> RedHat  = 1Mbs
    RedHat   <-> Windows = 1Mbs
    Debian   <-> OpenBSD = 1Mbs

    Debian   <-> RedHat  = 200Kbs ???
    Debian   <-> Windows = 200Kbs ???

A couple of things to note:

    - every machine on the LAN gets 64Kbs to the outside world, that is the
      cap on my DSL modem; this is fine

    - apart from the Debian box, when any machine on the network is talking
      to any other machine on the LAN, the speed is about 1Mbs. This too is
      fine.

Now for the weird part:

    - the Debian box gets 1Mbs when talking to the OpenBSD box, but only
      200Kbs when talking to the Windows or RedHat box. What gives?

Normally, I would think something is wrong with the NIC on the Debian box,
but it talks to the OpenBSD box fine. Can anyone explain this anomaly?

I have tried the following to no avail:

    - hooking up the machines to different ports on the switch

    - making sure the network cables aren't running parallel and causing
      interference

    - checking the NICs, each NIC that touches the switch is set to full
      duplex, and the one card on the OpenBSD box that talks to the DSL
      modem is half duplex

Any other suggestions?

thanks,
thomas

-- 
N. Thomas
nthomas@cise.ufl.edu
Etiamsi occiderit me, in ipso sperabo