Wi-Fi - Troubleshooting - BBA

Possible causes for a failure to connect to a Wi-Fi network?

1. Channel overlap, 2. Frequency mismatch, 3. security type mismatch, 4. issues associated with signal/power levels

When figuring out the scope of a wireless networking problem, it is useful to place the problem into one of three categories. What are the categories?

1. Client can't access shared resources (Web pages, remote folders, etc.). Client may or may not think it's on the network, but it can't access anything. 2. Connection is too slow. Client can access shared resources, but access is too slow. 3. Client's wireless connection is doing weird things.

Why is frequency mismatch rare nowadays?

Automatic channel selection is now the norm. Always set your wireless device to auto channel selection.

What is the first step in troubleshooting a Wi-Fi network?

Break the task down into logical steps. Start with identifying the scope of the wireless networking problem.

What is meant by saying "avoid physical issues" when remedying a wireless connection issue associated with too low WAP signal power?

Carefully identify possible dead spots when planning WAP placement. There is something physical in the way that keeps the signal from reaching its destination. When installing a network, watch out for concrete walls, metal (e.g. metal studs), and the use of RF-blocking window film.

Provide an example of channel overlap and a remedy.

Configuring an SSID, but setting each WAP only one channel apart e.g. channel 3 overlaps with channels 1 and 2. Remedy? Use only channles 1, 6, and 11.

What does CompTIA mean by security type mismatch when talking about troubleshooting problems with Wi-Fi?

1. You have set up the wrong encryption type when manually connecting to a Wi-Fi network, or 2. you have automatically accessed a particular SSID and entered the wrong passphrase.

What is meant by "incorrect antenna type" when troubleshooting a wireless connection?

In most cases, the default antennas (omnidirectional) used by WAPs are fine, but sometimes a different antenna type is better suited for the situation (e.g. one or more unidirectional antennas).

When discussing wireless networks, what is the classic no-errors-but-won't-work issue?

In older operating systems, you would often only get one chance to enter a passphrase when connecting to an SSID. If you failed to enter the correct passphrase, the only clue was that your client got an APIPA/zeroconf address. With newer operating systems, you actually get a message like "wrong passphrase."

What does it mean to use wireless scanning tools to check for wireless channel utilization?

Using software tools to retrieve metrics and reports about nearby devices and which ones are connected to which WAPs. They enable you to discover overworked WAPs, saturated areas, and so on, so you can deploy WAPs to optimize your network.

Which versions of 802.11 are more likely to have connection issues caused by channel problems?

older 802.11 versions that rely on 2.4 GhZ channels

Symptoms that a WAP's power levels are too low?

reduction in performance and, or failure of a client to access the network

Symptoms that a client is too far from the WAP?

reduction in performance and, or failure to access the network

It is likely on the exam that you will get questions about the limits set for Wi-Fi standards. This includes...

throughput speeds, frequencies, distances, and channel usage.

Every wireless client is set to DHCP, but if you enter the wrong passphrase, you won't...

get past the WAP to talk to anything on the network including the DHCP server (hence, your client will get an APIPA address)

If your WAP lacks signal power, you have five possible remedies. What are they?

1. get closer to the WAP, 2. avoid physical issues, 3. turn up the power, 4. use a better antenna, 5. upgrade to a new version of 802.11 (e.g. 802.11ac) with features that enable more efficient power usage.

Remedy for wireless connection problems associated with a client being too far from the WAP?

1. move the client closer to the WAP, 2. extend the distance capability of the network by adding one or more WAPs, 3. boosting the power of the WAP

Symptoms of a security type mismatch (when attempting to connect to a wireless network)?

1. not on the network, 2. continual prompting for the password, 3. APIPA/zeronconf address

Signs of a failure to connect to a Wi-Fi network?

1. repeated prompt for a password, 2. APIPA address, 3. etc.

Although changing antenna types and aggressive tweaking of antenna placement is a common troubleshooting technique when trying to overcome deadspots and similar issues, IT professionals can upgrade their WAPs to newer versions of 802.11 as a likely effective solution. What does an upgrade to 802.11n or 802.11ac offer that can help so well with connections issue?

MIMO and MU-MIMO not only drastically increase signal distance, they can also automatically fix otherwise tricky problems.

How do you turn up the power on a WAP?

Most manufacturers have low preset settings for radio power levels. Higher end WAPs (e.g. from Cisco) offer the ability to change those settings, but very few low-end SOHO WAPs offer that capability through the OEM interface. If you're willing to gamble, there is third-party firmware (e.g. OpenWrt) which works on some devices.

What is meant by "incorrect antenna placement" when troubleshooting a wireless connection?

Sometimes, just moving an antenna a few inches away from an obstacle can make big changes in performance.

Always remember to do what after installing a Wi-Fi network?

Test it i.e. verify the installation. Move some traffic from one computer to another using the network.

What is frequency mismatch?

This is a type of Wi-Fi connection problem that arises when the SSID is set correctly, but a device is using a different channel than the WAP.

What is channel overlap?

Wi-Fi connection problem that arises when 2.4 GhZ channels overlap with their nearest channel neighbors.

Remedy for a security type mismatch (when attempting to connect to a wireless network)?

enter the right password

Which is the most common type of security type mismatch?

entering the wrong passphrase