Troubleshooting & Validating Configurations

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 serial interface is DCE or DTE}
  • show ip dhcp binding {If the router is configured as a DHCP server}
  • show running-config {Make sure to press the space bar to show additional pages if the CLI says “–More–”}

Validating Your Lab is Functional and 100% Accurate

Validating your lab not only requires you to successfully ping between hosts on every network, but also requires you to scrutinize the output of “show running-config” and other commands to make sure every IP address, mask, routing protocol, network address, etc., are 100% accurate, and the required configurations exists.

With simulation software, some functions may work, although the configuration is not 100% correct. Accuracy in the configuration must always be your goal.

Pay attention to every detail!!!

Troubleshooting the configuration and interfaces

  • Scrutinize the output from “show running-config” and make sure 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
  • Are both Status and Protocol up on all router interfaces in use?
    • # show ip interface brief
  • Did you check the clockrate on the DCE interface is set, and greater than zero?
    • # show controllers s0/0 or s0/1

Routing Protocols

  • Did you add only the directly connected networks to the routing protocol?
  • Does “show ip route” list the correct number of routes based on the network topology/instructions?
  • Were the correct # of directly connected networks added to the routing protocol, and are the network addresses and masks correct?
  • When you configured the routing protocol, did you use the network address or an interface’s IP address?
  • When you configured OSPF, did you use the wildcard mask or the subnet mask?

PC’s

  • On each PC, is the Default Gateway an IP address on the “local network”?
  • When you ping a host or router, where is the ICMP request failing to get to its destination or is the target failing to respond?

Deciphering Ping/ICMP Responses

  • Destination host unreachable
    • The IP address returned by “Reply from” should be the destination IP address.
    • If it’s the IP of the Default Gateway, then the router doesn’t have the destination network in its routing table.
  • Request timed out
    • The packet is routed to the destination network, but the specific IP/host isn’t responding or doesn’t exist.
    • Does the destination host have the correct gateway address configured?

Example

For a PC on the 196.42.99.0 /24 network, with a Gateway of 196.42.99.1.5, and the destination is missing from the routing table:

  • Reply from 196.42.99.1.5: Destination host unreachable.

Still having problems? And you’re confident your configuration is correct? Then Save the lab, exit the simulation software, and then reload the lab.

Document the configuration of each router in your lab

How to save the output from commands on a router

  • Create a new TXT file with the same filename as the simulation file you’re documenting.
    syntax: CST3607 Lab-04 LastName, FirstName v<version #>.txt
  • At the top of the TXT file, type your CST3607 Lab-04 <YourLastName>, <YourFirstname>
  • Paste the output from all routers into the one TXT file:
    1. Make sure all routers have uniquie names: e.g. hostname 2621-A, 2621-B, etc.
    2. Close and reopen the CLI, to clear its history.
    3. enable
    4. terminal length 0
    5. show ip interface brief
    6. show ip route
    7. show ip protocol
    8. show ip ospf neighbor {If using OSPF}
    9. show controllers s0/0 or s0/1 {If the router is using a DCE interface}
    10. show ip dhcp binding {If the router is configured to be a DHCP server}
    11. show run {Make sure to press the space bar to complete the listing if the CLI says “More”}
    12. Select all the text in the CLI, then right-click, and choose copy. (Ctrl+a)
    13. Switch to your TXT file, and paste
    14. Save the TXT file.
    15. Repeat for each router in the lab.
  • Send the TXT file with all router configurations to me: Subject: CST3607 Lab-04 YourLastName, Firstname