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I upgraded my Internet connection, and after changing the Modem my Ubuntu Server's eth0 doesn't come up.

I looked at /etc/netwrork/interfaces, it looks all normal eth0 is set to auto and dhcp

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet dhcp

In the boot process right after Ubuntu starts to run, the lights for the port to which the cable is connected to stops blinking as if no cable is connected to it.

And that's when Ubuntu is trying to configure "virtual network devices".

It then tries to configure the network devices a couple of times taking about 2 minutes, then it says "Booting system without full network configuration".

dmesg | grep eth, shows two eth0: link downs, and one eth0: link is not ready.

When I do ifconfig I don't get an IP.

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What kind of modem did you add? Do you have anything interesting in dmesg | grep eth? Can your provider see your new modem through their tools yet? Is it in the process of downloading and installing firmware upgrades? – sarnold Feb 26 '13 at 1:01
My PC, MAC, PS and iPhone are all happily connected to the Internet, so it's probably not firmware or anything else with the modem. dmsesg | grep eh, shows eth0: link down, and eth0:link is not ready. When booting up I see "Booting system without full network configuration" after 60 second delays. – user893730 Feb 26 '13 at 1:12
The modem is Sagemcom 2864A, could the problem be with creating the loop back? does the modem have to allow it or something? And do I need "virtual network devices" ? – user893730 Feb 26 '13 at 1:18
Please edit your question to provide additional information - don't put it in comments. – guntbert Feb 26 '13 at 21:06

Unbelievable but restarting the modem fixed the problem, it seems to me like this modem has issues with DHCP, it almost crashes after making changes to DHCP, but restart fixes the issues.

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