Some time ago we published a blog post on why having separate SSIDs for 2.4 GHz and 5 GHz Wi-Fi bands was a bad idea in general. Much to our surprise, this became one of the most viewed blogs on our site! Seems to be a topic of interest, right? If you found the previous post useful, here's some more information.
As the original post explained, lots of (generally consumer-grade) Wi-Fi gear let you create one Wi-Fi profile and then assign per-band SSIDs to this profile, with innovative names such as "Greenhouse-2.4" and "Greenhouse-5". And the post also explained why this wasn't such a great idea:
- This defeats the ability of the Wi-Fi clients to automatically trade off rate and range: at close distances, they are set up to use the much more efficient and faster 5 GHz band, whereas at longer distances they switch to 2.4 GHz for better range
- This also prevents the clients' capability to detect and avoid interference and congestion - for example, a congested 5 GHz band (yes, there is such a thing) might result in a client automatically moving to 2.4 GHz to spread the load around, but forcing it to use a specific band prevents this
Here are a few more reasons why you shouldn't assign different SSIDs to the same Wi-Fi profile (effectively, VLAN) for different bands, based on our actual in-field observations:
- 'Sticky' clients. You might think that if you provide the clients with both the 2.4 GHz and 5 GHz SSIDs and passwords, the clients will automatically select the proper SSID depending on band conditions. Guess again. Clients are smart, but not _that_smart. They tend to be 'sticky': if they've connected on a given SSID in the recent past, they will often prefer that SSID when reconnecting, often in preference to a much better choice. (Actually this is not as brain-dead as you think it might be: switching to a new SSID commonly entails switching to a new IP subnet and DHCP scope, which would necessarily break all TCP connections and cause minutes-long delays. So it is better to stick to the same SSID as long as possible, in the interest of continuity.) The result is that switching from a 'bad' 2.4 GHz SSID that was in use at long range to a 'good' 5 GHz SSID that is now better because it's closer, isn't going to happen without a lot of false starts and probably even a manual intervention. NOT what you want for a good Wi-Fi experience.
- Inefficient roaming with multiple APs. Clients move from place to place (that's why we have Wi-Fi, after all). In the home, there's usually just one Wi-Fi AP, so it doesn't matter where they move to; you are either connected or not. In an office environment, there can frequently be multiple Wi-Fi APs, so that clients can seamlessly switch between the best APs as they move about the office - i.e., they roam. Splitting up the SSIDs by band puts a crimp in the roaming process: the clients can either roam between 2.4 GHz radios, or between 5 GHz radios, but not both. This is not optimal. We want to allow the client to pick the best AP radio available to it at all times, which might be 2.4 GHz in the hallway and 5 GHz in the conference room. Ergo, use the same SSID across all radios and bands.
- Management headaches. SSIDs are strings that need to be matched exactly by clients in order to connect. We've seen plenty of cases in a multi-office situation where one office had "xxx-5G" and the other office had "xxx-5" and some other office had "xxx-5 G" (note the space) and so on and so forth. This doesn't make for a good employee Wi-Fi experience, because the SSIDs look pretty much the same (to human eyes) and yet the profile that worked at the first office doesn't work at the second. (And it gets even more exciting when the passwords are inadvertently set differently at the different offices!) Uplevel setups fix this by enforcing the same SSID string and password for ALL bands at ALL offices - we've never had a complaint about 'my Wi-Fi profile isn't working'. But if you start appending the band to the SSID, this just makes it harder.
All this being said, there IS a case we have found where it was actually necessary to split the SSIDs between 2.4 GHz and 5 GHz bands (or at least have an SSID broadcast only on one of the bands and not the other): IoT devices (and printers, sometimes). There are IoT devices that we have run across that will pretend to support both 2.4 GHz and 5 GHz ... but when allowed to choose between them - same SSID on both bands - the device completely fails to connect. This is not a Wi-Fi feature. It is a bug in the IoT device itself. However, have you ever tried getting the vendor to fix it? (Have you ever tried trying to get through to the vendor?) It is usually easier to create a dedicated SSID for that device on the 2.4 GHz band that is NOT broadcast on 5 GHz, and then the device works fine.
This is just about the only case where splitting up SSIDs between 2.4 GHz and 5 GHz was a useful thing. In all other cases, not at all!
