Wireless troubleshooting can encompass a lot of variables. There's the wired network. There's the client supplicant configuration. There's client drivers. There's the authentication server. There's the wireless hardware. There's the wireless firmware. There's external WiFi factors. There's external non WiFi factors. There maybe configuration at multiple points. There's the physical layout of the APs themselves. And many more could surely be listed. And still a lot of the time wireless can be pretty forgiving and just work well enough to not be resolved.
With everything WiFi troubleshooting encompasses I was recently reminded of some troubleshooting basics. It was a simple and straightforward issue: an AP at a new site that wouldn't join to the controller. Everything that could have been suspect had been looked at: VLAN, routing, DNS, DHCP, swapping in new AP hardware, etc. By all appearances everything should've just worked. The AP would power up just fine, the controller was reachable by ping, their wasn't a firewall port stopping traffic, the controller GUI was working. Having discovered what it wasn't narrowed down what it might be. A few more minutes of troubleshooting led to the diagnosis: a bad ethernet cable. The cable was providing power to the AP, but the data pairs weren't passing traffic. A simple solution for what had been a time consuming problem.
What can help in troubleshooting problematic scenarios? I've found the CWNP troubleshooting methodology as described in the Certified Wireless Analysis book to be very helpful. This system has been designed to look at issues in a logical and systematic procedure. In summary the procedure is described as:
- Identify the problem.
- Discover the scale of the problem.
- Define the possible causes of the problem.
- Narrow to the most likely cause.
- Create a plan of action or escalate the problem.
- Perform corrective actions.
- Verify the solution.
- Document the results.
