The dilemma of Wi-Fi DFS Channels

Activate ? Do not activate? Learn more about DFS channels to make the right choice for your network

In order to better understand this mechanism, we will go through its history, its advantages and disadvantages so that we can better choose when configuring a Wi-Fi network for professional or domestic use.

A Meraki AP / Credits : meraki.cisco.com

The limits of the 2.4 GHz band

The 2.4 GHz band used with the popular 802.11b/g standards in the early 2000s quickly became limited, partly due to the limited number of channels, and partly due to the arrival of Bluetooth and consumer wireless devices such as home automation and many others.

Channels 1, 6 and 11 do not overlap (they are called “non-overlapping”) in 802.11b/g/n standard.

A new 5 GHz band, new rules

An additional band has emerged as necessary to cope with the increasing number of connected devices: the 5 GHz band.

The new channels available with the introduction of the 5 GHz band (ETSI)
  • The access point is in manually set channel mode : the DFS deactivates the AP.

DFS Parameters

What can be done?

Know your environment and its use

A dense environment (e.g. building, store) will benefit from additional channels (with DFS) to reduce interference on adjacent channels by better distributing the channels allocated to the access points. The same applies if a bandwidth greater than 20 MHz is chosen, in order to increase throughput.

Monitor DFS Events

Radars are not only located at airports or military zones, hence the interest in monitoring the frequency of “DFS Events” to judge the stability or not of the network at a given location. Unfortunately, it is often difficult to predict in advance whether an area will be subject to radar interference.

A DFS Event logged into Meraki Dashboard

Personal opinion

Activating DFS channels has far more advantages than disadvantages, particularly in terms of the large increase in the number of channels available.

python getMerakiEventCount.py -p wireless -t dfs_event -o 549236

Using default timespan : 1 day
Timespan : between 2020-11-14 16:37:07.722869 and 2020-11-15 16:37:07.722869
Network : DevNet Sandbox ALWAYS ON , Number of dfs_event : 17
Network : DNSMB3 , Number of dfs_event : 0
Network : DNSMB2 , Number of dfs_event : 1

References

To go further on the subject, I recommend the following sources of information:

Network Engineer @Decathlon. CCNA certified & DevNet in progress