When You Should Use Dynamic Frequency Selection in a Router (and When You Shouldn’t)



In your Wi-Fi router’s control panel, you may find a setting called “Dynamic Frequency Selection” (DFS) and wonder what exactly it is for and whether you should use it. Here’s when to use it (and some good reasons to avoid turning it on).

What is dynamic frequency selection?

If you’ve never heard of dynamic frequency selection before, don’t be too hard on yourself. If you’re not willing to read standard radio technical documents or look through the router’s menus with a magnifying glass, you’re unlikely to find it.

And even if you’re the type to look closely at every menu, dynamic frequency selection didn’t start appearing routinely in consumer router menus until the widespread deployment of 5GHz Wi-Fi routers – DFS was not necessary when everyone had 2.4 GHz-only routers. Even today, not all routers have DFS because the inclusion of the channel mapping standard requires additional certification and hoops for manufacturers to pass.

So what exactly is it and what does it have to do with Wi-Fi? The 5 Ghz Wi-Fi found in your home and anywhere else modern Wi-Fi hardware is deployed uses a portion of the radio spectrum that is part of a much larger communication band known as the “Band”. C”.

Band C is an important part of the microwave radio frequency band that goes from 4 Ghz to 8 Ghz. Several different portions of that range are used for all sorts of things, including satellite communications, military and civilian radar, weather radar, cellular communication, and more.

A weather radar dome and an example of a weather radar reading.
National Oceanic and Atmospheric Administration

Among the wide variety of things in Band C, the most common thing that overlaps with the same 5Ghz range used by Wi-Fi devices is weather radar. If you’ve ever heard your local weatherman on the news talking about “Doppler radar” results, he’s referring to information collected using the Terminal Doppler Weather Radar (TDWR) system that is widely used in the United States and around the world. to detect storms and dangerous weather conditions.

Network hardware noise interfering with critical things like weather radar is naturally not ideal. That’s where dynamic frequency selection comes into play.

DFS is a channel assignment scheme that was first introduced in 2003, as part of the IEEE 802.11h amendment to the 802.11 wireless standards, specifically to address this particular problem: Wi-Fi communication overlaps and potentially interferes with wireless communications. most critical radio.

In theory, this is beneficial for everyone involved. Consumers can use part of the C-band for their home Wi-Fi when radio waves are clear, and part of the C-band is returned when more important services are needed. In practice, it’s not exactly a free-lunch situation for consumers, and implementing DFS in the real world can be a blessing or a pain. Let’s take a look at when you should and shouldn’t use it.

What are the pitfalls of dynamic frequency switching?

Access to an otherwise inaccessible portion of the Wi-Fi spectrum sounds like an overall win for consumers, right? So why wouldn’t you want to use DFS to get more out of your router?

Typically, when DFS is available on a router, it is disabled by default and must be enabled. This, right off the bat, should tell you that most of the major router companies like Linksys, ASUS, etc think it’s a setting best used politely and as needed, and not turned on everywhere. .

So, before you immediately log into the control panel and start looking for settings, let’s take a closer look at the benefits and the pros and cons. Before we dive in, we want to start this section by saying that we’re deliberately pointing out the potentially frustrating things about using DFS so that you’re well prepared to work around it and consider whether you even want to use it before you just start using it.

DFS isn’t inherently bad, but if you don’t know all the little nuances of how it works and what it looks like while it’s active on your network, you could end up tearing your hair out trying to figure out why your Wi-Fi is. The Fi network just doesn’t work as expected.

Your router stays inaccessible longer after reboot

Aside from the obvious potential problem with DFS, which can interfere, however briefly, with more important radio traffic, the real reason router companies generally use offsetting by default is because of the headaches it can cause to customers.

Yes, when DFS is active, the router can use the part of the 5GHz band that overlaps with other services. And yes, that can significantly improve the Wi-Fi experience for the end user.

But DFS is required to run a check, called a Channel Availability Check, before using the specific channels in that range. This verification can take between 1 and 10 minutes, depending on the channel being verified within the restricted DFS range.

During this verification period, the 5 GHz network for the access point running the verification is unavailable, and if possible, it will revert to the 2.4 GHz network or simply remain unavailable until the verification is complete.

If the airspace is clear and the particular channel passes the channel availability check, after 1-10 minutes of Wi-Fi, the hotspot will be available to us. Every time you reboot your router and access points, you will have X minutes of downtime while the verification runs.

Your router changes channels when it detects interference

To comply with DFS rules, whenever your router or access points detect something that appears to be interference from a higher priority source in the DFS-allocated portion of the spectrum, a rapid sequence of events unfolds.

The router quickly blocks all clients on that channel, stops using the channel, broadcasts new information to local clients to guide them to the new channel, and traffic resumes. Additionally, the router adheres to a No Occupancy Period (NOP) of at least 30 minutes (although most consumer routers often leave the channel unused for longer, possibly until the next day).

When the Non-Occupancy Period has passed, the router will repeat the Channel Availability Check, albeit in an abbreviated form, before potentially switching to the new channel. As with the original longest boot time scan, the router will be inaccessible to wireless clients on the 5Ghz band during this time.

Because DFS is specifically designed with the goal of making some of the wireless spectrum accessible to consumers while protecting critical airspace for other tasks, it has a hair trigger when it comes to detecting interference.

The slightest bit of traffic on the restricted frequencies will cause your router to download it immediately. There is no back and forth, no confirmation if the traffic is actually weather radar or something, the DFS system immediately refers to the other traffic and switches.

Not all clients support dynamic frequency selection

There is no requirement that a client support dynamic frequency selection, nor indeed that a router or access point support it.

To use DFS spectrum channels, a manufacturer must comply with regulations regarding such use and obtain certification, but the simple fact of not offering the functionality is, in itself, a form of compliance with the restrictions for that part of the spectrum. radio spectrum.

This, of course, can present connectivity issues on your network. Changing DFS on some clients may have improved performance, while others suddenly have connection issues.

However, before leaving this section on the dangers of dynamic frequency selection, there is one positive noteworthy. With each generation of hardware, both on the router and on the client side, DFS handling is getting better. While you still sometimes notice strange interruptions or network behavior, more and more you don’t notice anything strange happening.

What are the benefits of dynamic frequency selection?

You might be thinking “Wow, that section on DFS cheats was pretty long…” and wondering if there is any reason to use it. But again, we’d rather you know what something is and if it’s right for you than just recommend it without dismantling it.

Dynamic frequency selection opens up significant additional headroom

We don’t want to completely discourage you from using DFS with your home router and access points. If you live somewhere with minimal to no interference from those restricted channels, they’re worth playing to access.

In the United States, the 5 GHz channel space includes 25 non-overlapping channels and 16 of them are in the DFS constrained space with a channel width of 20 Mhz. When you move to wider channel widths, such as 40Mhz and 80Mhz widths, the channels get wider and the number of available channels decreases. At 40Mhz there are only 4 non-DFS channels and at 80Mhz there are only 2 non-DFS channels.

So if you’re not in an area where radar or other interference routinely sends your router into the DFS evasion routines we described earlier, enabling it opens up roughly two-thirds of the 5GHz Wi-Fi spectrum available for your use.

It’s certainly nothing to sneeze at and is worth investigating if you’re unhappy with your router’s current performance and/or if you have a lot of Wi-Fi devices on your network.

Be warned though, if you’re not happy with your router, the problems are likely to be more numerous and bigger than limited channels. Check out some of our tips to improve your Wi-Fi signal, and be open to upgrading your router altogether.

Dynamic frequency selection shines in dense environments

If you live in an area chock full of other Wi-Fi signals from adjacent condos or apartments, it’s worth messing with DFS on your router for more reasons than one.

Not only is it ideal to have more channels for gaming in a very dense Wi-Fi area simply because the more airspace for all the different competing networks the better, there’s an even more “sneaky” reason, so to speak, to turn on DFS.

Assuming you’re not really near an airport or weather station that will immediately mess up your DFS expansion plans, turning on DFS when you’re in a Wi-Fi-dense apartment complex is practically free real estate.

Remember we talked earlier about most manufacturers shipping their hardware with DFS disabled? If you turn it on, you will most likely be the only person in your entire apartment building with DFS enabled. This means that all the other routers are screaming at each other in a fairly limited portion of the 5GHz Wi-Fi range, while your router will be able to spread freely in the almost completely empty DFS portion.

And hey, even if you don’t live in a dense apartment or live relatively close to an airport, feel free to experiment. There’s no chance that turning on DFS will break your router, screw up your Wi-Fi devices, or cause anything more than a temporary inconvenience if you don’t like the potential downtime or performance hits.

If DFS terminates without making your 5GHz network work better or you experience irritating issues like your computer or console losing connection while gaming, simply go back to your router’s control panel and turn it off.