xl(4) & polling

Rob spamrefuse at yahoo.com
Tue May 10 19:34:27 PDT 2005

Ruslan Ermilov wrote:
> Greetings,
> Those of you wishing to try your xl(4) card under
> polling(4) are welcome to test this patch:


Yesterday I discovered that polling of the xl
interface randomly disrupts an ssh-tunnel of mine.
I think there's still a subtle, yet critical problem
with xl polling.

I cannot locate the details of the problem, so I
will describe the symptoms that I see in my network,
and why I suspect xl polling.

Here is a sketch of my two private networks:

 PC1 - GW1 ~~~~ GW2 - PC2

   PC1 = PC on private network, Intel Pro/100 (fxp)
   GW1 = Dual-homed Gateway, 2 x 3Com 3c905B-TX (xl)
   GW2 = Dual-homed Gateway, 2 x RealTek 8139 (rl)
   PC2 = PC on private network, RealTek 8139 (rl)
   ~~~~ = Internet

All computers are running 5-Stable, as of May 10.
All, but PC1 with fxp, use polling, with:
   options HZ=1000

GW2 redirects (with natd) port 2200 to PC2.

PC1 establishes an ssh-tunnel to PC2:
  PC1$ ssh -p 2200 -N -f -R 2000:localhost:22 GW2

Then on PC2, I can use this tunnel to connect
directly to PC1, for example to run xbiff:
  PC2$ ssh -Y -p 2000 localhost xbiff

This works beautifully, but every now and then the
ssh-tunnel connection is 'closed' for no reason
(the ssh-tunnel itself remains, but the connection
is closed).
This happens at least once an hour, seemingly at

After some trial and error, I discovered that the
polling of the xl devices (GW1) is the culprit.

As soon as I disable the polling for the xl devices
on GW1, the ssh-tunnel connection is not disrupted


GW1 is also a production server, so experimenting
is rather limited. However, I can run tests, if that
would help resolve the problem.

Here you can find some relevant info on GW1 with the
xl devices:

dmesg output:
kernel configuration:


Yahoo! Mail Mobile 
Take Yahoo! Mail with you! Check email on your mobile phone. 

More information about the freebsd-stable mailing list