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Validation tools and troubleshooting



Tools

In previous blogs, we discussed the survey tool, but there are other tools to validate a network. It is important to document items such as the validation, what and why it is tested, which methods are used, what are the end results and did the results meet the requirements. Document the requirements as well and recommendations based on the results.

Spectrum analysis will locate interferences and measure the duty cycle of a channel. If the duty cycle is high, this can occur or indicate load handling problems. It is pretty common to use a spectrum analysis during your site survey. The side kick from Ekahau has a built-in spectrum analyzer. Spectrum analysis does not only show the duty cycle, but also the Real time FFT that shows the RF energy for each frequency at the moment, or the waterfall/spectrum density shows the most congested frequency band. Some shows also the channel duty cycle which is a percentage of time that the RF is busy.

Protocol analyzers can help you to identify the applications that are running on the network. Some protocol analyzer programs can already translate the type of protocol to the type of application that is in use. For example, when the program recognizes the protocol HTTP or HTTPS traffic, it indicates it as web application. Another example is VoIP protocols. There are protocol analyzers programs that can generate reports that help with analyzing quicker. For instance, the number of retransmits shown on the report can indicate that there is ACI.

Throughput testers can validate if the network is working as it should be. You can see the SNR, the packets per second, CRC errors, drops and retries. It depends on the brand that you use which features are visible. Some throughput testers are only command based, like iPerf.

Troubleshooting

When you discover some issues during the validation, you need to troubleshoot this. In one of my first CWAP blogs, I wrote about the troubleshoot methodology. This methodology is a couple of steps to help you during the troubleshoot process.

OSI model is a very important part for troubleshooting. If you start at layer 1 you check if the hardware is okay and if the cables are plugged in correctly. If you cannot connect to one specific access point, swap it with a spare and try it again. If clients can connect with the access point, but still are not able to access applications on the wired network, check the cables, wall outlet and patch panel. A spectrum analysis of the wireless network is also part of layer 1 troubleshooting. If all this is okay, go a step up and check layer 2, the switch configuration, VLANs and port security. At layer 3 you check the router configuration, whether there is an IP address, or if there is a routing issue due to some misconfiguration of routing protocols. When you see no issues on the first three layers, you know that the network is working fine. The issue can then be related to the client or application.

The issue can be a software issue or a hardware issue. If nothing works, and all applications fail, then there might be a problem in the hardware. If the laptop cannot connect to any network or you do not see any networks available then the issue might be the wireless network card. When it is just one application that is not working and all the others are working fine, it is probably an issue with the software of that specific application. This can be the software version that is not supported. So, the issues can be at the application server. Another server issue is that the DHCP/LDAP/RADIUS server is down or some client misconfiguration (client uses PEAP, but RADIUS supports EAP-TLS or the wrong passphrase). With DHCP you see that the client does not receive an IP address. With RADIUS server down or passphrase wrong, you will see that the client cannot logon to the network. Other issues can be bad cables, outdated firmware, or client adapter/driver issues. It is important to ask the right questions. What happened, when does it happen, where does it happen, is it with specific users or application or devices are good questions to start with. Never assume anything! Sometimes it is just try a solution and see if it is fixed.

To give an idea per problem area, here are some types of problems that can occur.

Coverage
- Display a weak signal
- Low data rates
- Not able to connect or maintain a connection
You can solve this with
- Adding more access points
- Increasing the output power
- Replacing antennas with higher gain antennas

Capacity
- High latency rates
- Low throughput rates
- Not able to connect
You can solve this with
- Adding more access points
- Implementing band steering and/or load balancing
- Disabling lower data rates

Roaming
- Dropped voice calls
- Corrupted video in live streams
- File transfer interruptions
You can solve this with
- Implementing PSK, OCK, 802.11r or other PMK cache mechanism

Security
- Cannot authenticate
- No security at all
- Server certificate invalid
You can solve this with
- Verifying passphrase or 802.1X/EAP type
- Does the client validate the certificate?

QoS
- Dropped or poor VoIP calls
- High latency or jitter rates
You can solve this with
- Verifying QoS configuration on all the devices. QoS needs to be end-to-end.

Beside those list of causes, check as well the data rate settings. Disabling the lower data rates can give some advantages, however, if there are clients that don’t support the higher enabled data rates, this client will not be able to connect to the network.