Strange problem with sk0

[Mikhail T.]

  Hello!

I have a rather bizarre problem with my on-board sk interface... It only 
works, when tcpdump is running...

Seriously. It negotiates with the switch (1000baseT/full-duplex) just 
fine, but, unless tcpdump has it open (and in "promiscuous" mode), no 
traffic seems to go through. It would not respond to pings -- not even 
from the switch itself, nothing.

But, as soon as I start tcpdump -- even if tcpdump never has anything to 
output:

    tcpdump -i sk0 -n src host 10.non.existent.IP

Traffic starts flowing just fine... Do I simply have flaky hardware? The 
motherboard is old, and, for some reason, I need to "remind" sk0, what 
its ethernet address upon reboote (it starts off with 00:00:00:00:00:00).

Any other explanations for what is happening? There are plenty of other 
systems (computers, VoIP phone, two TVs) on this switch and all are 
fine... I did try different ports on it -- same results. I also tried 
forcing things down to 100/half-duplex -- no change...

Thanks! Yours,

    -mi