SY0-301 · Question #292
Which of the following protocols uses TCP instead of UDP and is incompatible with all previous versions?
The correct answer is D. TACACS+. TACACS+ is the only AAA protocol in this list that uses TCP port 49 and was redesigned from scratch, making it intentionally incompatible with TACACS and XTACACS.
Question
Which of the following protocols uses TCP instead of UDP and is incompatible with all previous versions?
Options
- ATACACS
- BXTACACS
- CRADIUS
- DTACACS+
How the community answered
(47 responses)- A6% (3)
- B2% (1)
- C2% (1)
- D89% (42)
Why each option
TACACS+ is the only AAA protocol in this list that uses TCP port 49 and was redesigned from scratch, making it intentionally incompatible with TACACS and XTACACS.
The original TACACS uses UDP and is a simpler, older protocol that lacks the TCP transport and encryption features of TACACS+.
XTACACS is a Cisco-proprietary extension of TACACS that also uses UDP and predates TACACS+, with which it is incompatible.
RADIUS uses UDP ports 1812 and 1813 and only encrypts passwords in the authentication packet, not the entire payload like TACACS+.
TACACS+ uses TCP port 49 for reliable, connection-oriented communication and separates authentication, authorization, and accounting into distinct functions. It was designed as a completely new protocol, intentionally breaking compatibility with TACACS and XTACACS to add full packet encryption and expanded functionality.
Concept tested: TACACS+ TCP transport and protocol incompatibility
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/sec_usr_tacacs/configuration/xe-16/sec-usr-tacacs-xe-16-book/sec-tacacs.html
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