Cisco ICND2 – Identify and correct common problems associated with IP addressing and host configurations

Troubleshooting local network issues:

First, from the computer ping the local loopback this will ensure the NIC is functioning correctly.

Second, ping the Default Gateway for example if this fails try and ping another PC on the same network.

To find the default gateway that is set (normally via DHCP) on a Windows machine Start > Run > Type cmd and enter – in the black box type “ipconfig /all” followed by enter. This will display information relating to IP, DNS, Default Gateway and Subnet mask.

If both pinging the default gateway and another PC fail and you have a working PC – verify the PC that isn’t working is in the same subnet by running an ipconfig /all and compare the IP, subnet mask and default gateway.

Tracert can be handy to see where the packets drop off and may help identify where the fault lies.

Try and ping (if have access) from router to router to test connectivity.

Most issues are configured with an incorrect IP, Subnet mask or default gateway. A good example of this is one I encountered recently. There was a PC that could talk to a printer offsite but not on site on inspecting further the printer had the wrong subnet mask, meaning when the PC was on site, the printer was in a totally different subnet to that of the PC – a quick amendment of the mask and boom it worked. Easily missed.

Always consult with network documentation to ensure IP addressing is correct with VLSM networks. As as last resort use a Subnet calculator such as Bitcricket beware you’re not allowed a calculator on the exam.


  1. Ping
  2. Ping another PC on same network to verify connectivity
  3. Ping Default Gateway (cmd> ipconfig all)
  4. Ping DNS servers
  5. Ping router to router
  6. Tracert to see where packets are dropped
  7. Check cables
  8. Consult with network documentation, if unsure use a subnet calculator