Just a guess since I didn't see you say you did this - if yum-autoupdate was turned on, you may have gotten a new kernel installed and not realized it. When you rebooted, the driver for the ethernet port that  you got installed for the old kernel probably would need to be reinstalled for the new kernel. (Drivers usually get tied to specific kernel versions by recompiling/relinking to match up to that kernel's interfaces.)

If you did reinstall the driver, then others' suggestions may be more appropriate.

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]] On Behalf Of Larry Linder
Sent: Friday, March 07, 2014 3:47 PM
To: [log in to unmask]
Subject: SL 6.4 Ethernet Port is dead - maybe

I am looking for a way to check the functionality of an Ethernet port on a 4 
mo old new system.   We use this box for number crunching and reducing data.
Since no one uses the desktop we left it as "Gnome" and set up network.  This also the same box we found the SL 6.x had a broken driver for the chip set.  
Thanks to some serious help we were able to download the driver for the Ethernet chip set and it worked for a long time.

After a power failure on a clear day we noticed that it would boot and run but 
no intranet.   The power failure was city wide for about 5 sec.  Just enough 
to turn on the UPS,s and EM Lights.

I have look on the net and there is a lot of people offering suggestions but nothing you can hang you hat on.  Most just reference a lot of applications.

Tried:
drop down's for "preferences" and network set up.  restart "network" & NetworkManagement" .  These look OK.

Apps:
"ifconfig"
etho:  says that it read a large number of packets and transmitted none.

"ss"
gives a lot of information but Its pretty criptic to say the least.

The Ethernet chip set is on the mother board and I hate to dismantel it replace the mother board and have the same problem.  I was looking for a way to test it with a loop back scheme and monitor the transmission with a scope.
The Ethernet chip set supports 10/100/1000 megHz.   Because of the size of the 
data sets we need the 1 g. rate.   We plan to upgrade our entire network to 1 
G router, and switches once this problem is resolved.
Only change one thing at a time.

Larry Linder