When Ubiquiti introduced airOS 8 back in 2016, the support to connect up the older airMAX M5 devices was added, with the release of airOS 6. However, there are some limitations in doing this that it is important to be aware of.
airOS 8 History
First of all, with earlier versions of airOS 8 there were a few options for setting up an access point. WIth airMAX AC, airMAX Mixed and PtP.
With later versions, this choice is much simpler, with only the option to set the device as an access point or a PtP device.
This now means that by default, an airMAX AC AP can have the older airMAX M devices be connected up, without the need for extra configuration.
Limitations & things to consider
However, due to the different generations of hardware, there are some technical limitations between airMAX AC and airMAX M.
The non standard 802.11 channel widths in use on airMAX AC are not compatible with airMAX M. It'll only work on 20MHz and 40MHz channel widths.
airMAX M stations can only be connected up when the AP is in Access Point mode, it won't work in PtP mode.
airMAX M devices support both WPA and WPA2, so when migrating older networks over, ensure everything is on WPA2 to ensure proper operation between AC and M.
AC devices need to be on airOS 8 or later and M devices need to be on airOS 6 or later.
Mixed Mode works on airMAX AC 2GHz and 5GHz, with connectivity between M2 and M5 devices.
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