I installed a Fedroa 9 system,when I cmd ifconfig,it shows "eth0 fetching interface information device not found".Then I opened the Network Configuration Window, in the option of "Hardware" it shows as flows:
Description:nVidia Corporation nForc
Type:Ethernet
Device:eth2
Status:system
if I reboot the system, the items up becomes:
Description:nVidia Corporation nForc
Type:Ethernet
Device:eth3
Status:system
and reboot the second time :
Description:nVidia Corporation nForc
Type:Ethernet
Device:eth4
Status:system
That's to say the Device'name changed as the times I have booted the system.
Anyone can help me? Thank you!

send me the content of the file /etc/modprobe.conf

I have solved the problem!
The problem was caused by a bad NIC,because its MAC address changed every time I boot the system.So I change the line in /etc/udev/rules.d/70-persistent-net.rules to the next:
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="??:??:??:??:??:??", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"
So whatever the MAC address is,its name always is eht0.