Troubleshooting Wireless LANs

Last Updated on July 9, 2018 by Admin

About The Module

No wireless LAN can escape the need for troubleshooting. Without careful preparation, planning, and design, wireless LANs can fail to perform optimally. Site surveys, RF modeling and tools are necessary to ensure an operational and performing wireless LAN. Environmental conditions and network usage change, equipment failures and software glitches occur. Good troubleshooting tools and a systematic approach can help isolate and resolve those problems faster.

This module covers the following topics:

  • Overview of Wireless LAN Troubleshooting
  • Understand and Dealing with Wireless Interference
  • Troubleshoot Wireless LAN Connectivity

This course contains the following pages:

  • Presentations: Eleven short recorded video presentations created by various presenters.
  • Additional Resources: Links to additional resources are also provided as a convenience to learners. The appearance of external links does not constitute endorsement by Cisco, nor does Cisco exercise any editorial control over the information found at these external sites.
  • Quiz: Brief quiz after each module to check your understanding of key concepts presented in each module.

Course Outcome

Upon completion of this module, you will be able to:

  • Understand systematic troubleshooting approach
  • Understand types of wireless interference
  • Understand Mitigation Technologies
  • Understand how to troubleshoot wireless LAN connectivity

Overview of WLAN Troubleshooting

Troubleshooting wireless LANs means troubleshooting space and obstacles in creative ways. Rather than contend with wire, you are contending with environment, furniture, walls, and RF interferences. This often arises as a result of not doing proper preparation, planning and design of the wireless LAN.

Troubleshooting Basics

It is important to understand some troubleshooting basics. Troubleshooting 101- we have to clearly define our problem.

In a wireless LAN environment, issues may occur with

  • the clients,
  • the access points,
  • the wireless LAN controller and code versions,
  • the placement of the access points or the clients, and the location in which they are trying to receive wireless signal.

We have to understand all the possible triggers. We have to know what the expected behavior is based upon normal proper operation. We have to test the environment, and be able to reproduce the errors that we are seeing. We then need to be able to analyze and redefine the problem, question the issues, rerun the tests and reanalyze.

Troubleshooting is a systematic method by which we do not just want to throw darts at the dartboard and hope that we find the issue. We do not want to jump into any conclusions either.

The various sections of this module will cover some of the key characteristics of troubleshooting, the areas to look for and a systematic approach of where one might want to start looking and then provide some solutions and remediations.

Non-802.11 Interference

Understanding the different types of interference that can affect wireless network communications is essential. In reality, there are many other types of devices emitting in the unlicensed band of 802.11 devices. These devices include microwave ovens, cordless phones, Bluetooth devices, wireless video cameras, outdoor microwave links, wireless game controllers, Zigbee devices, fluorescent lights, WiMAX and so on. These non-802.11 types of interference typically don’t work cooperatively with 802.11 devices, and can cause significant loss of throughput.

Types of RF Phenomena

The radio frequency (RF) environment is complex and dynamic. RF interference can be a major inhibitor to wireless performance, creating security vulnerabilities and wireless network instability.

Fresnel Zone

When designing and installing an outdoor wireless point-to-point bridge, it is generally thought that line of sight is required. But there is also a requirement for clearance of what is known as the Fresnel Zone (named after French physicist Monsieur Fresnel).

Spectrum Analyzer

In an RF environment, if we suspect that we have interference, reachability, range, or quality issues, we will want to deploy a spectrum analyzer to detect and manage the interference. Spectrum analyzers are designed to detect and measure RF energy that is present in the environment

Spectrum Analyzer Example

The author provides an overview at the Meraki RF Spectrum and Air Marshal technology in the video.

Cisco CleanAir Technology

Cisco CleanAir technology integrates spectrum analysis into wireless access points to provide real-time, always-on visibility into external non-802.11 sources of interference present in the environment.

The CleanAir solution not only detects the source of interference, but also automatically changes the channel on which the wireless network is operating to a channel clear of interference. This is done with a spectrum analysis chip that resides within Cisco CleanAir Access Points.

Client Connectivity

There is a sequence of required conditions in order for wireless client connectivity to be established. Understanding the various stage of the client connection as it process through the sequence will help identify where issue arise.

Using Tools

Tools are one of the ways that help with diagnose and troubleshooting of client connectivity.

Access Point Connectivity

Troubleshooting Access Point connectivity involves both wired and wireless connectivity. A wireless access point has to be physically connected to a wired infrastructure, therefore any issues with either the wireless or wired infrastructure can cause connectivity to fail.

Using Tools

The same tools that are used for troubleshooting client connectivity can be used for troubleshooting access point connectivity. There are some handy tools available on smart mobile devices that can serve simple troubleshooting purpose.


When deploying wireless networks, these are the important considerations:

  • Ensure proper preparation and planning before implementing the wireless network. This will help to eliminate a lot of unnecessary troubleshooting and problem solving. Generally most issues are related to bad signal strength, poor reachability and lack of client connectivity.
  • Know the physical environment. Having knowledge of everything in the environment during site surveys and plan the access point locations. This helps eliminate access point issues, with the signal strength and with client connectivity. Understand the materials that are used in the walls of the building or site, what the cubicles are made of, what is in the warehouses, what the surrounding external building materials are, how high the ceilings are etc. All of these will help in providing a better preparation and plan.
  • Invest in tools to help with the planning, such as AirMagnet or Ekahau, and RF spectrum analysis tools. Some of these tools are included in the Cisco wireless infrastructure products, wireless LAN controller, Cisco Prime Infrastructure, and in the Meraki dashboard, providing wireless management and troubleshooting aids. There are other third-party spectrum analysis tools such as inSSIDer and NetSurveyor from ‘Nuts about Net’ and others.
  • Understand what the client devices are being used for, what type of client devices are being used, such as smartphones, tablets, laptops, warehouse scanners for inventory control and what their wireless capabilities. That way you can ensure that your client devices and access points are supporting the same wireless protocols, such as 802.11ac.
  • Be prepared to make changes to the deployment. The environment may change or the client needs change. Often, after the deployment of wireless network is done, an organization may need to remodel a particular floor, change the way the offices are laid out, add new walls to separate rooms, warehouses where they change the direction of storage rack. All these changes are going to impact the wireless network and result in a need to troubleshoot issues that arises. Be prepared to make changes to the deployment when there are changes made in the environment. When a client uses a different protocol, be prepared to make changes. Sometime, the wireless network may need to be scaled up due to the density of clients. More access points might need to be added. Adding new applications such as voice over IP wireless may change some of the deployment too.