What is difference between tacacs and radius?

 TACACS+ uses the Transmission Control Protocol (TCP) and RADIUS uses the User Datagram Protocol (UDP). Some administrators recommend using TACACS+ because TCP is seen as a more reliable protocol. Whereas RADIUS combines authentication and authorization in a user profile, TACACS+ separates the two operations.

RADIUS	TACACS+
Combines authentication & authorization.	Separates all 3 elements of AAA, making it more flexible.
Encrypts only the password.	Encrypts the username and password.
Requires each network device to contain Authorization configuration.	Central management for authorization configuration.
No command logging.	Full command logging.
Minimal vendor support for authorization.	Supported by most major vendors.
UDP- Connectionless UDP ports 1645/1646, 1812/1813	TCP- Connection oriented TCP port 49
Designed for subscriber AAA	Designed for administrator AAA

Many vendors support the TACACS+ protocol, including Adtran, Alcatel/Lucent, Aruba,

Brocade/Foundry, Cisco/Linksys, Ericsson/Redback, Extreme, Fortinet, Fujitsu, HP/3Com,

Huawei, Juniper/Netscreen, Netgear, Nortel, and others.