TACACS+
termnetworkingsecurity
A protocol for centralising administrative access to network devices, separating authentication, authorization and accounting into distinct exchanges.
The separation is the practical difference from RADIUS: because authorisation is its own exchange, a device can ask the server about each command as it is typed, which is how per-command control and full command logging work. That makes it the usual choice for device administration while RADIUS remains usual for network access. The dependency deserves stating - if the server is unreachable and local fallback was never configured or never tested, the estate becomes unmanageable at exactly the moment somebody needs to log in.
Also known as: tacacs plus