Wireless Troubleshooting · Topic 3 of 3
Wireless Diagnostic Tools
Learn the RouterOS wireless diagnostic tools such as scan, snooper, spectral scan, sniffer, alignment, bandwidth test and torch, and when to use each one.
- 4 min
- Scan lists nearby networks, and snooper shows channel usage and the stations on each channel.
- Frequency monitor shows how busy each frequency is.
- Spectral scan sees non Wi-Fi interference and needs supported hardware.
What it is
Diagnostic tools are the RouterOS features that show what is happening on the air and on the link.
Each tool answers a different question. One shows nearby networks, one shows channel use, one captures frames and one measures speed.
Knowing which tool to pick is more useful than knowing every option of every tool.
How it works
The tools fall into three groups: those that look at the air, those that look at frames and those that test the link.
Looking at the air
| Tool | What it shows |
|---|---|
| Scan | Nearby networks, their channels and their signal |
| Snooper | Channel usage, and the networks and stations seen on each channel |
| Frequency monitor | How busy each frequency is over time |
| Spectral scan | The energy on each frequency, including non Wi-Fi sources, on hardware that supports it |
/interface wireless scan wlan1
/interface wireless snooper snoop wlan1
/interface wireless frequency-monitor wlan1
/interface wireless spectral-scan wlan1Scan and snooper interrupt normal service, because the interface stops serving clients while it listens. Run them with care on a live access point.
A scan on a busy access point drops its clients for the time it runs. Do it when users are not affected, or use a spare radio.
The spectral scan is the only one of these that sees interference from devices that are not Wi-Fi. It needs a radio that supports it, and not every model does. On the wifi driver, the scan command is /interface wifi scan, and the available tools can differ from those on the legacy package.
Looking at frames
The sniffer captures wireless frames so you can study them in detail.
/interface wireless sniffer set interface=wlan1
/interface wireless sniffer start
/interface wireless sniffer stop- The capture can be saved to a file or sent to a remote analyser.
- The captured frames show management exchanges such as authentication and association.
Use a capture when a join fails and the log is not enough. It shows who sent which frame and how the other side answered.
Aligning an antenna
The alignment tool helps point a client antenna at an access point. It shows the signal while you move the antenna, so you can find the best direction.
/interface wireless align interface=wlan1This is most useful for long links with directional antennas.
Testing the link
These tools test the path, not the radio only.
| Tool | Use |
|---|---|
| Ping | Checks that the other end answers, and shows delay and loss |
| Bandwidth test | Measures the throughput between two RouterOS devices |
| Torch | Shows the traffic crossing an interface, per address and protocol |
/tool ping 192.168.88.1 count=5
/tool bandwidth-test address=192.168.88.1 direction=both
/tool torch interface=wlan1The bandwidth test generates a lot of traffic, so it affects other users. Run it when the network is quiet.
Run a bandwidth test in both directions. A big difference between transmit and receive often points to interference at one end or to different antenna conditions.
Choosing a tool
Match the question to the tool.
- Which networks are near me? Use scan.
- Which channel is least busy? Use snooper or frequency monitor.
- Is a non Wi-Fi device interfering? Use spectral scan.
- Why does the join fail? Use the log, then the sniffer.
- Is the antenna aimed well? Use alignment.
- How fast is the link? Use the bandwidth test.
- What is using the bandwidth? Use torch.
What to remember for the exam
Seven facts cover this topic.
- Scan lists nearby networks, and snooper shows channel usage and the stations on each channel.
- Frequency monitor shows how busy each frequency is.
- Spectral scan sees non Wi-Fi interference and needs supported hardware.
- The sniffer captures wireless frames for detailed analysis.
- The alignment tool helps aim an antenna.
- Bandwidth test measures throughput, and torch shows the traffic on an interface.
- Scan and snooper interrupt the clients of an access point while they run.
Common mistakes
These four errors are common.
Running a scan on a busy access point. The clients are disconnected while it runs.
Expecting scan to find non Wi-Fi interference. Only the spectral scan sees it.
Testing speed with only one direction. The two directions can differ.
Running a bandwidth test during busy hours. It uses a lot of bandwidth.
Check yourself
Work through these three questions.
Which tool shows interference from devices that are not Wi-Fi?
The spectral scan, on a radio that supports it. Scan and snooper show only Wi-Fi networks.
What is the effect of running a scan on a live access point?
The interface stops serving clients while it listens, so they are disconnected for the time it runs.
Which tool measures throughput between two RouterOS devices?
The bandwidth test, with
/tool bandwidth-test. It is best to test in both directions.
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