Cisco CCNP Certification exam tutorial – Knowing RADIUS and TACACS for your ISCW Exam

by Chris Bryant - 19 May 2008

Cisco switchesAs part of your CCNP certification exam studies, particularly for the ISCW exam, you need to be very clear on the differences between TACACS+ and RADIUS.

As a CCNA and future CCNP, you’ve already configured authentication in the form of creating a local database of usernames and passwords for both Telnet access and PPP authentication. This is sometimes called a self-contained AAA deployment, since no external server is involved.


It’s more than likely that you’ll be using a server configured for one of the following security protocols:

TACACS+, a Cisco-proprietary, TCP-based protocol

RADIUS, an open-standard, UDP-based protocol originally developed by the IETF

An obvious question is “If there’s a TACACS+, what about TACACS?” TACACS was the original version of this protocol and is rarely used today.

Before performing AAA Authentication configuration, there are some other TACACS+ / RADIUS differences you should be aware of:


  • While TACACS+ encrypts the entire packet, RADIUS encrypts only the password in the initial client-server packet.
  • RADIUS actually combines the authentication and authorization processes, making it very difficult to run one but not the other.
  • TACACS+ considers Authentication, Authorization, and Accounting to be separate processes. This allows another method of authentication to be used (Kerberos, for example), while still using TACACS+ for authorization and accounting.
  • RADIUS does not support the Novell Async Services Interface (NASI) protocol, the NetBIOS Frame Protocol Control protocol, X.25 Packet Assembler / Disassembler (PAD), or the AppleTalk Remote Access Protocol (ARA or ARAP). TACACS+ supports all of these.
  • RADIUS implementations from different vendors may not work well together, or at all.
  • RADIUS can’t control the authorization level of users, but TACACS+ can.

We’ll discuss the uses of both of these protocols in a future CCNP certification tutorial! Look for more CCNA, CCENT, and CCNP tutorials right here on this same website!


Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of free CCNA certification exam tutorials.

Security+ exam tutorials are also available, as well as Network+ certification exam materials and tutorials!

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