Exam Topic 1.1 – Use Cisco IOS Troubleshooting Tools
As a Cisco Certified Network Professional, let loose among the networks of the world, you’re going to need a toolkit to get to the bottom of the issues you’ll face. Documentation is one such tool that will prove invaluable to you, it’s a tool I am guilty of not using to its fullest potential and that’s why I’m listing it first here.
Documentation Tools
Network Diagrams – It may sound obvious, but network diagrams are invaluable when you encounter a problem. It may be a problem with your own network, it may be a problem on a network you’re being hired in to troubleshoot. Valid, up-to-date network diagrams will help you get to the bottom of whatever is going on. Personally, I create diagrams in Visio packed with as much detail as I can squeeze in without the diagram becoming a mess.
Ticketing Systems – However you want to describe this tool type, be it Help Desk, Service Desk, Trouble Tickets etc. This tool will help you understand the breadth and severity of a problem. Is it one person affected? Is it a department, a site, a whole datacentre? Not only will you receive a ticket describing a problem and who is affected, but you can add updates to the ticket to inform others of what you’ve done and see what others have done in kind. This prevents double-handling of tasks and will help get to the bottom of a problem faster, while keeping stakeholders informed of progress.
Documentation Storage – So you have diagrams, and you have a ticketing system, but without some method of collating it all, what use is it? This is where the likes of Sharepoint, MediaWiki or Netbox come in. Netbox is a particularly good option for network engineers as it’s a solution written by and for network documentation. Circuits, IPAM (IP Address Management), Rack space, among other things can all be recorded in a web-based application with access restricted to those who need it.
Basic Tools
CLI Tools – The network engineers bread and butter. Get comfortable with using the CLI for troubleshooting and you will fare well in the field of networking. Here’s by no means an exhaustive list of examples of CLI tools:
- show run
- show ip interface brief
- show ip route
- ping <IP address>
- trace <IP address>
- debug ip ospf events
GUI Tools – Cisco has a few GUI tools available to end users to assist with configuration and/or troubleshooting, none of which are tested in this exam, but they are worth mentioning so you’re aware of their existence. Tools like Cisco Configuration Professional (CCP).
Recovery Tools – When recovering from equipment failure, you’ll need replacement gear with the correct software image on it, but you’ll also need a copy of the config that was running on the failed kit. Some Cisco kit allows you to back up your running and/or startup config to a TFTP, FTP HTTP or SCP server. This can be done manually, it can be scripted or you can utilise a built in Archive tool which will generate the config for you and move it to the transfer server du jour.
Logging Tools – Device logs are a gold mine of information when it comes to troubleshooting time. Searching through device logs on console can be time consuming though and you don’t always get the whole picture if the device log has a small buffer set. Exporting your logs to a Syslog server, allows you to peruse your logs for your devices with the assistance of filters using fields such as time, device, IP address etc. Logging occurs in 8 severities ranging from 0 to 7 as can be seen below:
| Severity Level | Name |
| 0 | Emergencies |
| 1 | Alerts |
| 2 | Critical |
| 3 | Errors |
| 4 | Warnings |
| 5 | Notifications |
| 6 | Informational |
| 7 | Debugging |
Note that Severity 7 log messages are only created when you have issued a debug command.
NTP – Though not used as a troubleshooting tool in itself, Network Time Protocol is a fundamental aid to your troubleshooting. Imagine having to troubleshoot a complex problem where your looking at the logs of different devices but the timestamps for each log entry are all messed up because the devices aren’t using NTP… For the sake of yours and any other poor souls sanity in the future, please use NTP to synchronise the date and time across all your devices!
Advanced Tools
SNMP – Simple Network Management Protocol allows for monitoring of important statistics from your devices such as CPU usage, memory usage, interface utilisation among other things. An SNMP server polls each device added to it every few minutes and over time, builds up a picture of the health of your network. So you can now see how busy an interface is. What if you want to know what’s eating up the bandwidth on that interface? Enter Netflow!
Netflow – Allows you to distinguish different conversations (flows) on your network, what protocol any given flow is using and who the talkers are involved in that flow and exactly how much data is being transferred. Netflow caches can be kept and read on any given individual device, but the most useful way of utilising Netflow is to export it to a 3rd party Netflow collector.
