Which of the following protocol was used by the INITIAL version of the Terminal Access Controller Access Control System TACACS for communication between clients and servers?

The correct answer is C. UDP. The original TACACS protocol, developed in the 1980s for ARPANET, used UDP (User Datagram Protocol) for communication between network access servers (clients) and the TACACS authentication server. UDP was chosen for its low overhead. The later XTACACS and then TACACS+ (a Cisco…

Submitted by renata2k· Apr 18, 2026Access Controls

Question

Options

ATCP
BSSL
CUDP
DSSH

How the community answered

(41 responses)

A
5% (2)
B
2% (1)
C
90% (37)
D
2% (1)

Explanation

The original TACACS protocol, developed in the 1980s for ARPANET, used UDP (User Datagram Protocol) for communication between network access servers (clients) and the TACACS authentication server. UDP was chosen for its low overhead. The later XTACACS and then TACACS+ (a Cisco proprietary redesign) migrated to TCP port 49, which provides reliable, connection-oriented transport. TACACS+ also encrypts the entire packet body (not just the password), unlike the original UDP-based TACACS. SSH and SSL are unrelated to the original TACACS transport layer.

Topics

#TACACS#AAA protocols#UDP#Access control protocols

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