Country and Regulatory Domain Settings · Topic 2 of 2
Country Code and DFS
Learn why the country code matters, how it controls channels and power, and how DFS radar detection works on 5 GHz channels, including CAPsMAN settings.
- 4 min
- The country code selects the allowed channels, the power limit and the DFS rules.
- In CAPsMAN the country is set in the configuration on the manager.
- Setting a different country does not make the radio legal there.
What it is
The country code tells a wireless radio which regulatory rules to follow, and DFS is one of the rules it enforces.
Each country decides which channels may be used, how much power is allowed and where radar protection is needed. The radio takes these limits from the country setting.
DFS stands for dynamic frequency selection. It makes access points on some 5 GHz channels listen for radar and move away when they hear it.
How it works
The country sets the rule list, and DFS forces the radio to share spectrum safely.
What the country code controls
The country code decides:
- which channels and frequencies the radio may use
- the maximum power on each channel
- whether a channel needs DFS
- in some countries, whether the rules differ for indoor and outdoor use
If the country is wrong, the radio may offer channels that are illegal at the site, or hide channels that are legal.
Setting the country
On the legacy wireless package the country is a parameter on the interface. In CAPsMAN it belongs to the configuration, so the manager decides it for the CAPs.
/interface wireless set wlan1 country=germany
/interface wifi configuration add name=cfg1 country=Germany- The first command sets the country on one legacy radio.
- The second creates a wifi driver configuration that carries the country.
In CAPsMAN you set the country once on the configuration, and every CAP that receives it follows the same rules. Check the value before you provision, because a CAP in a different country than the manager would need a different configuration.
Setting a country you are not in does not make the radio legal. It only changes the rule list the radio applies.
Why DFS exists
Some 5 GHz channels are shared with radar systems, such as weather radar. Wi-Fi may use these channels only if it gives way to radar. This is the job of DFS.
These channels are called DFS channels. Channels that do not need radar detection are non DFS channels, and a client or access point can use them at once.
How DFS works
DFS has three steps.
- Channel availability check. Before using a DFS channel, the access point listens for radar for a set time. During this time it sends no traffic.
- Monitoring. While it runs, the access point keeps listening for radar.
- Moving away. If it hears radar, it leaves the channel at once and picks another one.
After a radar detection, the channel cannot be used again for a fixed period, known as the non occupancy period, which is 30 minutes.
The availability check delays the start of the network. The delay is about a minute on most channels, and longer on a few. Clients may not see the SSID until the check ends.
DFS settings in RouterOS
On the legacy wireless package the dfs-mode parameter controls radar detection. The value radar-detect listens for radar and moves the channel when needed.
/interface wireless set wlan1 dfs-mode=radar-detect frequency=autoIn legacy CAPsMAN the channel profile has a skip-dfs-channels option, which tells the manager not to pick DFS channels. The wifi driver channel profile has a skip-dfs-channels option too.
| Choice | Result |
|---|---|
| Allow DFS channels | More channels, but a start up delay and possible radar moves |
| Skip DFS channels | Fewer channels, but fast start up and stable operation |
Use DFS channels when you need more channels. Skip them where a fast and steady start matters more, for example for voice.
What to remember for the exam
Seven facts cover country and DFS.
- The country code selects the allowed channels, the power limit and the DFS rules.
- In CAPsMAN the country is set in the configuration on the manager.
- Setting a different country does not make the radio legal there.
- DFS makes an access point on certain 5 GHz channels detect radar and leave.
- The access point listens before it starts, and no traffic is sent during that check.
- After radar is detected, the channel is blocked for 30 minutes.
- Skipping DFS channels gives a faster start but fewer channels.
A CAP that boots slowly on a 5 GHz DFS channel is behaving normally.
Common mistakes
These four errors are common.
Choosing the wrong country. The channel list and power limits then do not match the site.
Expecting an instant start on DFS channels. The channel check delays the network.
Forgetting radar moves the channel. Clients may drop for a moment when the access point changes channel.
Setting the country on each CAP. In CAPsMAN the manager configuration should carry it.
Check yourself
Work through these three questions.
What does the country code control?
It selects the allowed channels, the maximum power and whether DFS is needed. Some countries also treat indoor and outdoor use differently.
What happens when a DFS access point hears radar?
It leaves the channel at once and picks another one. The old channel is blocked for 30 minutes.
Why might you skip DFS channels in CAPsMAN?
Skipping them gives a faster start and stable operation. The cost is that fewer channels are available.
Topic 2 of 2 in Country and Regulatory Domain Settings
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