Subject: Re: Problems with wm interface and vlan's
To: Chris Ross <>
From: Steve Woodford <>
List: netbsd-users
Date: 03/02/2005 14:04:29
On Wednesday 02 March 2005 04:59, Chris Ross wrote:
>    I have an i386 machine running NetBSD 2.0.1.  It is running almost
> without
> problem, but the network performance on it is pitiful!

>    1) When I use fxp0, the MTU of the vlan interfaces are 1500, just
> as is
> the mtu on fxp0.  But, when I use wm0, I have to manually set the mtu
> to 1504,
> because if I don't, the MTU on the vlan interfaces comes up as 1496
> when they are created.  Why is this different?

Looking at the source for wm(4), it appear that models before i82543 do 
not support the 1504 byte packets required for VLAN tagging. This is why 
the vlan(4) reports an MTU of 1496. If you don't tweak the MTU to 1504, 
does everything work fine? If not, perhaps you are blocking ICMP, which 
will break path MTU discovery.

>    2) What can I do to test what the problem is with my wm0?

What does the kernel dmesg say about the wm(4) card at attach time?

>    I looked at the Cisco switch it's hooked into (in both cases), and
> it does report input errors from the wm.  But, it doesn't indicate
> what type they are.  Can I get error counters from the card under
> NetBSD?

Try netstat -i. You may also consider dropping the cisco's MTU to 1496...

> Could it be a software problem in the kernel, or is it a 
> hardware problem?

It's more than likely a limitation of your particular wm(4) card.

Cheers, Steve