This seems to happen occasionally, and at the worst possible time. These are the steps I normally take to diagnose and solve the problem on a wired connection. It is assumed that the connection worked properly at some time in the past.
There is no special setup for this example, unless you happen to have a broken machine somewhere. You can run most of these commands without fear of hurting a good system.
Try these steps when diagnosing a network issue:
First let's make sure the connection is really down by pinging a known external address. I use Road Runner as my ISP, so for me the command would be:
ping rr.com
Something like this should appear:
Press
Find your gateway address. Run the
route
command; your gateway should show up at the top of the output. Note, theroute
command...