fxp entering promiscuous mode causing link to bounce

[Ian Smith]

On Fri, 16 Mar 2012 16:49:54 -0400, Mike Tancsa wrote:

 > I dont recall seeing this on RELENG_7, but I dont have a box to test 
 > with anymore confirm. On one box I upgraded to RELENG_8 I just 
 > noticed the nic will bounce if I enable tcpdump on it.  Sure enough, 
 > trying on a different RELENG_8 box with an fxp nic shows the same 
 > result.
 > 
 > eg
 > 
 > tcpdump -ni fxp0 -c 20
 > 
 > fxp0: link state changed to DOWN
 > fxp0: promiscuous mode enabled
 > fxp0: link state changed to UP
 > fxp0: link state changed to DOWN
 > fxp0: promiscuous mode disabled
 > fxp0: link state changed to UP
 > 
 > I verified it on 2 different boxes. Is there a way to prevent this 
 > from happening ?

Confirmed on 8.2-RELEASE.  I hadn't noticed as I tend to use tcpdump -p

Mar 17 14:00:03 t23 kernel: fxp0: link state changed to DOWN
Mar 17 14:00:03 t23 kernel: fxp0: promiscuous mode enabled
Mar 17 14:00:05 t23 kernel: fxp0: link state changed to UP
Mar 17 14:00:14 t23 kernel: fxp0: link state changed to DOWN
Mar 17 14:00:14 t23 kernel: fxp0: promiscuous mode disabled
Mar 17 14:00:16 t23 kernel: fxp0: link state changed to UP

I've also noticed that it consistently takes a couple of seconds after 
enabling or disabling promisc mode before coming back UP here.

There were several updates to fxp between 7 and 8.0 through 8.1-STABLE 
upto 8.2-R, concerning UP/DOWN occurrence and timing at boot, around 
suspend/resume and dhclient.  I'd been watching it with some suspicion 
regarding a suspend/resume issue (that turned out to be usb-related).

cheers, Ian