Given a scenario, troubleshoot common wireless problems. This chapter covers different wireless technology topics that might cause problems during the network implementation and maintenance phases, including signal strength and interference, incompatibilities, encryption, and SSID mismatches. Learn more in our Certified Wireless Network Associate (CWNA) video course.
Wireless Problems – Signal Issues
When working with a wireless network, you have to consider that transmission is based on radio waves, so anything that might influence radio wave transmissions might create problems for the wireless network. Interference and problems might come from many places, and you have to consider all of them in the wireless troubleshooting process.
Some interference can be avoided before actually launching the network into production by doing a site survey. This process can determine whether other wireless networks are operating in the same air space and, if so, you can avoid the channels they are using. You need to plan this site survey before implementing the network to make sure you avoid some major known trouble areas.
There are also some things that will be completely out of your control. For example, if you are in a very large building, your network might have to coexist with other equipment that resides in that area. You cannot complain about this because wireless networks operate on public frequencies that are managed by the local authorities. For example, in the U.S., public frequencies are managed by the Federal Communications Commission (FCC). In addition, there are other parts of those frequencies that might overlap with other services. For instance, the amateur radio service has access to some of the same 2.4 GHz frequencies that you might use in your wireless network, so this is another factor that might influence the network. In such situations you have to do a proper analysis and decide how you should manage your network.
Interference is a very common problem related to wireless signals. Your wireless network might be affected by devices that operate on the same radio frequencies and if this is the case, you need to find the sources of interference and shut them down.
You also need to think about signal strength in terms of different components that might impact it, for example:
- Transmitting signal
- Transmitting antenna
- Receiving antenna
Another signal-related topic involves the channels you are using, which is another type of signal issue you have to keep in mind. On wireless networks, there are a number of channels that you can use and you might have some systems that have been manually configured to use an incorrect channel. The effect is that they are getting either poor performance or no throughput at all.
In a standard wireless environment, you also have to think about bounce and latency. One problem might involve signals bouncing off of the flat objects that exist in the area, which will create latency when the signals reach the central antenna. Another problem is multi-bounce interference, where the signals are received by the AP but they arrive at different times. Flat surfaces can create issues but there are a number of things you can do from an architectural perspective to avoid problems involving bounce and latency.
You might also have issues where the access point was originally installed in the wrong place, maybe far away from the users. To solve this you need to move it somewhere else to ensure optimal signal strength in that specific area. This is usually established in the site survey and measurements phases.
One of the things that you should do to minimize interference is to find all possible sources that might affect your wireless network, including:
- Cordless phones
- Microwaves ovens
- High-power sources
- Florescent lights
You can test those sources and see what type of interference you might have, but you may not have a lot of control over them in terms of both locating and disabling them in a multi-tenant building. To test for interference, you can use performance monitoring software or a dedicated portable device that can analyze all the radio frequencies in a specific area. In extreme cases you may want to invest in a hardware spectrum analyzer that can look over the entire frequency range and give you more detailed results visually, including where each wireless signal is generating from and the exact location of the interference. After completing the site survey, you can decide on the best place to position your access points.
Using the tools presented above and a clear design strategy will help you to avoid major sources of interference so that you have the best wireless signals possible.
Wireless Configuration Issues
When working with wireless access points and trying to configure them, you can modify a number of different configuration options available. Misconfigured options can lead to undesirable effects and problems in your infrastructure. An access point configuration process is generally divided into two parts:
- Configuring wireless access for the users
- Configuring uplink options, either to the wireless LAN controller or to the WAN connection
In the first part, configuring wireless access for the users might involve enabling wireless functionality, setting the channels and other parameters, and configuring a DHCP pool. The second part includes properly configuring the access point uplink toward the network infrastructure and making sure that the access point correctly carries user traffic to the rest of the network.
In large environments, where you have more than one access point, you need to make sure that all of the access points have the same SSIDs configured, so as people move across one side of the building to the other they can seamlessly move from one AP to the other, without traffic interruption. If you name one of the access points with an incorrect SSID, users will not be able to seamlessly move and connect to the right access point. Again, make sure that you configure the correct SSIDs throughout the network.
In a large environment with many different devices, you may have some devices running on 802.11b, some of them running on 802.11g, and others running on 802.11n. There can be multiple reasons for this, including the use of old devices that cannot be upgraded from 802.11b. For this reason, make sure that you configure the access points to be backward compatible. Some APs are configured to work on 802.11n only, so if you don’t change this default setting, other devices that are running 802.11g or 802.11b will not be able to connect to that access point. There is usually some kind of configuration change you can make to allow that AP to operate on many different standards at the same time.
You also have to think about the type of encryption you will use between the access points and the wireless network users. Every device in the network must be configured exactly the same way and use the same encryption type, for example:
- WPA
- WPA2
- WPA2 Enterprise
If you are in an enterprise environment and you are planning to integrate a back-end authentication server, you should configure it using WPA2 Enterprise. You also should make sure that the encryption keys are identical, especially if you have multiple access points. In addition, make sure that your SSIDs are the same and that you are using the same encryption type so that users can seamlessly move from one AP to the other.
Once the wireless network is installed, you should confirm that the configuration settings are working as expected by analyzing the signal coverage, and then determine whether the configuration setting that you made for a particular frequency will work well in that particular environment. You can also see if there is any potential interference that might require access point configuration changes. As mentioned before, using a spectrum analyzer can give you a graphical view of the associated wireless parameters. Having all of these tools available will ensure that you have exactly the right configuration on your access points.
Wireless Network Analyzer – SOHO Router
Wireless network analyzers can come in many forms. One type has integrated functionality in wireless routers or access points. Figure 11.1 below illustrates the wireless network discovery functionality in a DD-WRT SOHO router:
Figure 11.1 –Wireless Network Analyzer
The information presented in the status table above includes:
- SSIDs
- MAC Addresses
- Channels used
- Transmission rates and the 802.11 protocols used
- Other Wi-Fi parameters (e.g., noise, beacon, etc.)
Another way of representing the same information is in graphical format, as presented in Figure 11.2 below. With this format you can identify the access points (SSIDs) and the wireless clients associated with them.
Figure 11.2 – Wireless Network Analyzer (Graphical Format)
Wireless Network Analyzer – Dedicated Software
When the environment becomes very complex, the recommendation is to use a dedicated professional wireless network analyzer. This type of analyzer can reveal a lot of information about the wireless transmitters in the area, and you can also obtain a graphical representation of the channels used, as illustrated in Figure 11.3 below:
Figure 11.3 – Wireless Network Analyzer (Dedicated Software)
Some of the important information included in Figure 11.3 is as follows:
- Wireless transmitter SSIDs
- Signal strength
- Channels used
- Security methods used
- MAC Addresses
- 11 protocols used
In addition to all this information, you also have a graphical representation of the channels used and the associated signal strengths for both 2.4 GHz and 5 GHz frequency ranges.
When working with a wireless network, you have to consider that transmission is based on radio waves, so anything that might influence radio wave transmissions might create problems for the wireless network. Interference and problems might come from many places, and you have to consider all of them in the wireless troubleshooting process.
Interference is a very common problem related to wireless signals. Your wireless network might be affected by devices that operate with the same radio frequencies and if this is the case, you need to find the sources of interference and shut them down.
You also need to think about signal strength in terms of different components that might impact it, such as:
- Transmitting signal
- Transmitting antenna
- Receiving antenna
One of the things that you should do to minimize interference is find all possible sources that might affect your wireless network, including:
- Cordless phones
- Microwaves ovens
- High-power sources
- Florescent lights
An access point configuration process is generally divided into two parts:
- Configuring wireless access for the users
- Configuring uplink options, either to the wireless LAN controller or to the WAN connection
You also have to think about the type of encryption you will use between the access points and the wireless network users. Every device in the network must be configured exactly the same way and use the same encryption type, for example:
- WPA
- WPA2
- WPA2 Enterprise
Netgear troubleshooting guide.
Configure Wireless in our 101 Labs – CompTIA Network+ book.
