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Saturday, January 30, 2010

Day 13: IP Address Troubleshooting

What if an IP address or subnet mask is entered incorrectly and your computer is configured to obtain an IP address automatically?

We could directly start at Layer 3 and use ping. If that's ok, there's probably an upper-layer issue. There could also be a DNS problem, I've already discussed it in my day 17 post.

Follow these steps on a Windows machine to verify the DHCP operation:
  1. Enter the command ipconfig /all in a command box. It should show lots of info like subnet mask, gateway, DNS server(s) and IP address.
  2. Are the gateway and host IP address on the same subnet?
  3. Release and renew the dynamic assignment with ipconfig /release and ipconfig /renew.
  4. If you can ping your gateway but no Internet address, there's a problem between your router and ISP (DNS, etc.). You could also use the tracert command (traceroute in IOS) to further investigate the issue.

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