[wellylug] Network cards running at 10mb/s instead of 100 - w hy?

[Ewen McNeill]

In message <1066628275.3089.29.camel at damon.asianreflection.com>, Damon Lynch wri
tes:
>On Tue, 2003-10-21 at 07:10, Ewen McNeill wrote:
>> Given the mii-tool output you list I'd be looking at what the card is
>> plugged into.
>
>[description involving cross over cables and PCI 4-port "hub card"]

FWIW, I've always been fairly dubious about the "NIC plus hub" cards.
Perhaps they're convenient for some people's networks, but just as I
like external modems, I like external hubs/switches. 

Having puzzled out your network a bit it appears to look like this:

  ['net]
     |
+---------+
| gateway |---------[DMZ machine]
+---------+
  | | | | 
        [Internal]

and you seem to have various links where one end is claimed as 10Mbps
and the other is claimed as 100Mbps (eg, DMZ machine has a 3c59x at
100Mbps, FD, connected to dmfe on the gateway at 10Mbps half duplex).
I'm surprised that works at all.

Crossover connections are prone to failures in negotitation, leading to
one end thinking the connection is at one speed, and the other at the
other speed.  This can cause all sorts of weirdnesses, particularly if
there is a duplex mismatch (full/half), that only show up under load.
(A crossover with a mix of half and full duplex links will work okay
under a small load, and really fall apart under high load, especially
with fast machines.)  Sometimes this means you have to force/lock the link
to a particular combination of settings (at BOTH ends) in a crossover
cable to get reliable operation.

In the "autonegotiate" state, it should pretty much be the hardware
determining everything, and the software just reporting it.  So if it's
not negotiating the right thing it's more likely to be a hardware issue
(or poor implementation of the negotiation). 

I'd be inclined to test things into a known-good (external) switch
before looking for software issues.  Especially given the "no link"
reports (which indicate that it's not getting the autonegotatiate/link
alive polls).

Ewen