Troubleshooting & Verifying Networks

Diagnostic Commands

Make yourself familiar with the output from each of these commands.

  • show ip interface brief
  • show ip route
  • show ip protocol
  • show ip ospf neighbor {If you’re using OSPF}
  • show controllers s0/0 or s0/1 {Determine if the router has a DCE interface}
  • show ip dhcp binding {If the router is configured as a DHCP server}
  • show running-config {Make sure to press the space bar to complete the listing if the CLI says “More”}

Troubleshooting & Verifying Your Lab

Verifying your lab not only requires you to successfully ping to and from hosts on every network, but also requires you to scrutinize the output of “show running-config” to make sure that every IP address, mask, routing protocol, network address, etc., are correct, and the configuration is 100% accurate.

With simulation software, some functions may work, although the configuration is not 100% correct, but may fail when used on a real/physical device. Accuracy must always be your goal.

Troubleshooting Steps:

  • Scrutinize the output from “show running-config” and make sure that all the configured values are correct.
    • Are the IP addresses and subnet masks correct?
  • Did you enable all the required interfaces on all the routers? # no shutdown
  • Have you checked all router interfaces in use to make sure both Status and Protocol are both up? # show ip interface brief
  • Did you check that the clockrate on the DCE interface is set, and is greater than zero? # show controllers s0/0 or s0/1
  • Did you add only the directly connected networks to the routing protocol?
  • Does “show ip route” list to correct number of routes based on the network topology.
  • When you configured the routing protocol, did you use the network address or the interface’s IP address?
  • When you configured OSPF, did you use the wildcard mask or the subnet mask?
  • On each PC, is the Default Gateway for the “local network” correct?
  • When you ping a host or router, where is the ICMP request failing to get to its destination or failing to return?
  • Still having problems? And you’re confident that your configuration is correct? Save the lab, exit the simulation, and then reload the lab.
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