I have multiple Access Points on the same network with a Radius server for authentication. When I switch from one AP to another, do I have to go through the complete re-authentication processes each time?
If your access points are independent, then yes, each time you connect to an access point, you need to authenticate. This happens automatically in the background but incurs some delay and the communication will be briefly cut.
This is one of the major issues with stand-alone APs.
To solve this, you can use access points managed centrally by a controller. In this case, you authenticate once and the controller manages the handover from an AP to another one with (almost) no delay.
It depends on how your access points are set up. If your access points are centrally managed by a wireless controller, then the wireless controller will synchronize authentication traffic from radius servers. The access points can reach the wireless controller for authentication every time it is required. The user won't experience an interruption when they are moving around in that wireless network.
In the case where access points are not integrated with a wireless controller then the access points have to authenticate the user every time the user switches access points
1Edited for clarity. Jul 16, 2020 at 12:45
3For example, these items should do seamless handoff: Cisco Wireless LAN controller and skinny Cisco APs, Ubiquitii software-based controller for Unifi APs, both in my experience, and I understand that HP procurve/Aruba, and such similar systems support handoff like this.– CriggieJul 16, 2020 at 20:22
1@Criggie Just about any wireless controller can handle this. It is one of the 3 main reasons they exist in the first place. The other ones are: 1) managing broadcast power and channel selection to the AP's don't interfere too much with each other and 2) provide central management of the whole wifi infrastructure.– TonnyJul 17, 2020 at 8:06