Single-factor
Multifactor
RADIUS
RADIUS stands for Remote Authentication Dial in User Service. It’s a common AAA (Authentication, Authorization, Accounting) protocol.
RADIUS allows for centralized authentication of users. For example, multiple devices like routers, switches, VPN concentrator, firewalls, etc can talk to and authenticate with the RADIUS server for server authentication, remote VPN access, and 802.1x network access.
RADIUS services are usually already built into most server operating systems.
TACACS
TACAS stands for Terminal Access Controller Access Control System. TACACS is an alternative to RADIUS. TACACS is also a remote authentication protocol.
A newer version of TACAS is called TACACS+. TACACS+ is an open standard and provides more authentication requests and response codes.
