We received a new server on Supermicro X9SCL/X9SCM motherboard with "Intel Corporation 82574L Gigabit Network Connection" Ethernet controller some time ago and installed Centos 6 on the box. Unfortunately the server was loosing network connection until some one reboots it. Luckily we have configured IPMI on the box so the issue could be investigated. As I found the problem is related to old e1000e network driver in RHEL 6 and Centos 6 2.6.32-71.29.1.el6 kernel.
How it looks after "ifconfig eth0" command :

Network service restart couldn't help as you may see on the picture above.
There were these messages in dmesg after network restart :
lo: Disabled Privacy Extensions
ADDRCONF(NETDEV_UP): eth0: link is not ready
You may try to stop udev, unload e1000e driver and load it again (kill udev process; rmmod e1000e; modprobe e1000e), but I really doubt that these actions could help without reboot.
From the other hand Intel have more fresh drivers but I am too lazy to compile them as kernel module, blacklist old drivers in kernel and add custom module with the new drivers.
There are new compiled e1000e drivers in Elrepo repository.
Elrepo e1000e drivers installation:
# wget http://elrepo.org/linux/elrepo/el6/x86_64/RPMS/kmod-e1000e-1.6.2-1.el6.elrepo.x86_64.rpm
# rpm -Uvh kmod-e1000e-1.6.2-1.el6.elrepo.x86_64.rpm
# reboot
Old drivers from RHEL kernel:
# dmesg| grep -A 1 'Network Driver'
e1000e: Intel(R) PRO/1000 Network Driver - 1.2.7-k2
e1000e: Copyright (c) 1999 - 2009 Intel Corporation.
Updated drivers:
# dmesg| grep -A 1 'Network Driver'
e1000e: Intel(R) PRO/1000 Network Driver - 1.6.2-NAPI
e1000e: Copyright(c) 1999 - 2011 Intel Corporation.
Если кому надо это же, только на русском языке - пишите в комментариях.
How it looks after "ifconfig eth0" command :

Network service restart couldn't help as you may see on the picture above.
There were these messages in dmesg after network restart :
lo: Disabled Privacy Extensions
ADDRCONF(NETDEV_UP): eth0: link is not ready
You may try to stop udev, unload e1000e driver and load it again (kill udev process; rmmod e1000e; modprobe e1000e), but I really doubt that these actions could help without reboot.
From the other hand Intel have more fresh drivers but I am too lazy to compile them as kernel module, blacklist old drivers in kernel and add custom module with the new drivers.
There are new compiled e1000e drivers in Elrepo repository.
Elrepo e1000e drivers installation:
# wget http://elrepo.org/linux/elrepo/el6/x86_64/RPMS/kmod-e1000e-1.6.2-1.el6.elrepo.x86_64.rpm
# rpm -Uvh kmod-e1000e-1.6.2-1.el6.elrepo.x86_64.rpm
# reboot
Old drivers from RHEL kernel:
# dmesg| grep -A 1 'Network Driver'
e1000e: Intel(R) PRO/1000 Network Driver - 1.2.7-k2
e1000e: Copyright (c) 1999 - 2009 Intel Corporation.
Updated drivers:
# dmesg| grep -A 1 'Network Driver'
e1000e: Intel(R) PRO/1000 Network Driver - 1.6.2-NAPI
e1000e: Copyright(c) 1999 - 2011 Intel Corporation.
Если кому надо это же, только на русском языке - пишите в комментариях.