kernel: rl0: watchdog timeout

[Luke Dean]

Since I upgraded to version 6, my server has frozen under heavy network 
traffic three times.  It ran happily for months on various versions of 
5.  Same hardware, same configuration.
There was never anything in /var/log/messages until this last time.  This 
time I found:

kernel: rl0: watchdog timeout

I don't know what it's trying to tell me, and I don't know if it's a 
cause or an effect.

This is 6.0-STABLE as of late Sunday night.  i386.  rl0 is my WAN-side 
interface.  vr0 is my internal interface.  This machine runs DNS, email, 
web, NFS host, and several other services.  It uses pf with altq.

I don't think the system is panicking.  It doesn't reboot.  It may be 
freezing.  It becomes unresponsive on both network interfaces.  When the 
incident occurs, there's always a lot of simple TCP/IP traffic that's 
just passing through the box (not NFS, email, web, or anything the box 
provides on its own) and my first response is to hit the reset button to 
get it going again.

What should I look for?
The handbook says to check cables, and they seem fine.