vr0 only working if tcpdump -n -i vr0 is running

[Jonathan Schleifer <js-netbsd-users%webkeks.org@localhost>]

Hi!

I'm having a strange problem with the vr0 in my barebone. It is only working 
when running tcpdump -n -i vr0 in the background. As soon as I stop it, it 
stops working again.

There are several things strange with this network anyway:

• I have to use a specific MAC, so I do ifconfig vr0 link $some_mac active
  first.
• Many NICs did not even get a signal, my WiFi access point only gets a signal
  sometimes, but if it got one, it keeps it. But until it gets one, I have to
  restart it several times. (I guess the cable is too long or something).

But for some reason, everything works fine when tcpdump -n -i vr0 is running. I 
solved it by now by adding ! /usr/sbin/tcpdump -n -i vn0 >/dev/null 2>&1 &. It 
does not take a lot of CPU, so it works, but I'd like to know what could be the 
reason that this is required?

I think it has something to do with tcpdump putting the device into promiscious 
mode. Does the promiscious mode change anything on the physical layer, or is 
this a kernel bug? Should I send a PR?

PS: Please CC me if you reply to tech-net, as I'm only subscribed to 
netbsd-users.

--
Jonathan