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Date:      Sun, 28 Mar 1999 13:31:01 -0500 (EST)
From:      Bill Paul <wpaul@skynet.ctr.columbia.edu>
To:        current@freebsd.org
Subject:   Re: 3com Nic Problems
Message-ID:  <199903281831.NAA04739@skynet.ctr.columbia.edu>
In-Reply-To: <000101be7941$1b2e3200$2300000a@a35.my.intranet> from "RT" at Mar 28, 99 12:33:33 pm

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Of all the gin joints in all the towns in all the world, RT had to walk 
into mine and say:

> Heres are the nic combinations I've tried in one machine:
> 
> 3com 905 (at 100mbit) & 3com 905b (at 10mbit)
> 3com 905b (at 100mbit) & 3com 905 (at 10mbit)
> 3com 905 (at 100mbit) & realtek 8039 (at 10mbit)
> 3com 905b (at 100mbit) & realtek (at 10mbit)
> 3com 905b (at 100mbit) & ne2000 (at 10mbit)
> 
> In each case the 3com operating at 100mbit failed to do so smoothly.  In
> some cases I receive device time-outs, on bootup "xl0 command not
> completed",

Ignore the command failed to complete message. It's not fatal. It's
amazing how many people get all flustered when they see this.

> and in some cases no warning at all..

It's timing dependent.

> 100mbit will peak at 4MB/s, then all of a sudden stop, then go racing off,
> then stop...

This is a classic "I didn't configure my card correctly" symptom.

For the Nth time, both sides of the link must use the same modes. You
can't mix and match speed and duplex settings like they're tuneable
parameters that you can tweak to get more performance. Both sides must
match. If they can't figure out how to match on their own using 
autonegotiation, make them match. (You're the one with the brain and
the reasoning skills after all. Well, that's the theory anyway.)

If you want two 100Mbps NICs connected back to back (via crossover
cable), then do the following on _both_ sides:

# ifconfig xl0 media 100baseTX mediaopt full-duplex

The symptoms you're describing indicate a condition where one side of
the link is set for full duplex and the other is set for half. This doesn't
work: when the NIC is in full duplex mode, it turns off the collision
detection logic (since in theory you're not supposed to have collisions
on a full duplex link). If one side is doing collision detection and
the other isn't, you tend to see 'stuttery' performance.

If you're connecting a NIC to a 10Mbps hub (that's hub as in repeater,
not a switch), then you must set the NIC for 10Mbps half-duplex:

# ifconfig xl0 media 10baseT/UTP mediaopt half-duplex

If you're connecting a NIC to a 100Mbps hub (again, that's a hub as
in repeater, not a switch), then you must set the NIC for 100Mbps
half-duplex:

# ifconfig xl0 media 100baseTX mediaopt half-duplex

If you're connecting a NIC to a 100Mbps switch port, then in theory
the switch port and the NIC will perform NWAY autoselection and get
the modes right on their own. Sometimes this fails though, in which
case you should manually configure the switch for the mode you want
and configure the NIC to match.

When you connect two NICs back to back and one of them supports NWAY
and the other doesn't, the NIC with NWAY autonegotiation support can
sometimes get the mode wrong. In this case, you should manually
configure the NIC with NWAY so that agrees with the other NIC's modes
using ifconfig as shown above.

The NE2000 and 8039 boards don't support full duplex. So if you
connect a one of these to the 3c90x NICs via crossover cable, then
you must force the 3Com nic to 10Mbps half-duplex:

# ifconfig xl0 media 10baseT/UTP mediaopt half-duplex

This is because the NE2K and 8039 (ne2k compatible) don't support full
duplex mode.

-Bill

-- 
=============================================================================
-Bill Paul            (212) 854-6020 | System Manager, Master of Unix-Fu
Work:         wpaul@ctr.columbia.edu | Center for Telecommunications Research
Home:  wpaul@skynet.ctr.columbia.edu | Columbia University, New York City
=============================================================================
 "It is not I who am crazy; it is I who am mad!" - Ren Hoek, "Space Madness"
=============================================================================



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