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I am having an impossible time figuring out why my new CentOS box is not getting internet connectivity. Strangely enough, it used to work fine and I did not change any of the configuration on my end before it mysteriously stopped working about a day ago.

I can activate and deactivate eth0 without any error messages. Looking at /var/log/messages, I see only a couple suspicious entries involving eth0.IPv4 and mDNS.

Does anybody have ideas for what the problem might be and how I go about debugging this?

A screenshot of the console is below.

console

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Start with trying to your default gateway by its IP. Can you reach that? Then try to ping a well know website. Does that work, does its name resolve to an IP? Then try a ping and a traceroute from outside your network to your host. Does it work? If not where does it break down? –  Hennes Sep 10 '13 at 19:31
    
Cannot ping the machine from another machine. Cannot ping yahoo.com, cannot ping the default gateway either, says 'destination host unreachable' –  user788171 Sep 10 '13 at 20:07
    
If you can not ping it from a host on the same LAN then your network is either down or misconfigured. Start there. If you can reach it from another machine on the same LAN but can not reach the default gateway then your problem in in the DG/route table. Please add 1) If you use an static IP or DHCP. 2) The output from ifconfig 3) the output from route -n –  Hennes Sep 10 '13 at 20:10
    
Ok, so I have fixed this now, believe it or not, it was actually a bad network cable!! –  user788171 Sep 11 '13 at 3:23

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