> Could you please post "ifconfig -m vr0" output and
> similar ifconfig output on the other side?
> I guess the abort errors are caused by excessive collisions,
> but it should not happen on full-duplex (or auto negotiation).

vr0:flags=8b43<UP,BROADCAST,RUNNING,PROMISC,ALLMULTI,SIMPLEX,MULTICAST> mtu 1500
        address: 00:04:61:4e:4d:ac
        media: Ethernet 100baseTX
        status: active
        supported Ethernet media:
                media none
                media 10baseT
                media 10baseT mediaopt full-duplex
                media 100baseTX
                media 100baseTX mediaopt full-duplex
                media autoselect
        inet 10.0.0.1 netmask 0xffffff00 broadcast 10.0.0.255
        inet6 fe80::204:61ff:fe4e:4dac%vr0 prefixlen 64 scopeid 0x3

The other computer run WinXP and the network card is a Realtek RTL8169/8110.
In the advanced settings, I've changed the NIC to have 100Mbps/Full
duplex(i've tried Half Duplex and Auto Negotiation too)

> Is the network usable except the kernel messages?

I've tried this multiple times, switching between 10baseT and
100baseTX(and interface down & up after this).  I also tried with
mediaopt full-duplex and without, that didn't seem to affect.  Most of
the time the connection doesn't work at all, but sometimes rarely it
works but very slowly.  When it's not working, I get messages to log:

May 19 18:06:24 reming /netbsd: vr0: transmit aborted
May 19 18:06:24 reming /netbsd: vr0: using force reset command.
May 19 18:06:26 reming /netbsd: vr0: transmit aborted
May 19 18:06:26 reming /netbsd: vr0: using force reset command.
May 19 18:06:28 reming /netbsd: vr0: transmit aborted
May 19 18:06:32 reming /netbsd: vr0: transmit aborted
May 19 18:06:46 reming /netbsd: vr0: receive error: incomplete frame;
size = 0, status = 0x600
May 19 18:06:46 reming /netbsd: vr0: receive error: incomplete frame;
size = 0, status = 0x600

When it's working, it's incredibly slow, and most of the pings time
out.  Nothing comes to log.

- Teijo