Not sure how many people have this issue, or if it's been discussed, but with my new system (Asrock A75 Extreme6), it has a RealTek onboard nic. Slackware detects it as an R8169 and uses that driver, when it should use the R8168b driver.
My log showed constant "link up" messages in the logs, sometimes as often as every 5 or 10 seconds.
I found this info to remove the R8169 driver and install the R8168b driver.
Download r8168B driver:
tar vjxf r8168-8.023.00.tar.bz2
Remove r8169 driver:
Now install the downloaded r8168B driver:
load the r8168 driver:
Blacklist the r8169 driver to prevent it from loading again.
echo "blacklist r8169" >> /etc/modprobe.d/blacklist.conf
Now verify that the r8168B driver has been loaded and is in use now:
I've had zero problems since following this. Just thought I'd pass it along for other AMD A8/Realtek NIC users.