hardMultiple SelectObjective-mapped
RADIUS vs TACACS+ Differences
Which three statements about RADIUS and TACACS+ are true? (Choose three.)
Quick Answer
The correct answer is that RADIUS uses UDP as its transport protocol, while TACACS+ uses TCP. This fundamental difference stems from how each protocol handles encryption and packet delivery: RADIUS encrypts only the password in the access-request packet and relies on UDP’s lightweight, connectionless transport for speed, whereas TACACS+ encrypts the entire packet body and uses TCP’s reliable, connection-oriented delivery to ensure complete message integrity. On the ENCOR 350-401 exam, this distinction tests your understanding of AAA architecture and is often paired with the fact that RADIUS combines authentication and authorization into a single process, while TACACS+ separates them into distinct phases. A common trap is assuming both protocols use the same transport or encryption scope—remember that RADIUS is “password-only” and UDP, while TACACS+ is “full-body” and TCP. For a quick memory tip, think “R-UDP” (RADIUS uses UDP) and “T-TCP” (TACACS+ uses TCP), and that TACACS+ encrypts the “Total” packet.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
TACACS+ encrypts the entire packet body, whereas RADIUS only encrypts the password.
The correct answers contrast the two protocols. Option A is correct because TACACS+ encrypts the entire packet body, while RADIUS only encrypts the password. Option C is correct because RADIUS combines authentication and authorization, while TACACS+ separates them. Option E is correct because RADIUS uses UDP (typically port 1812/1813), while TACACS+ uses TCP (port 49). Option B is wrong because RADIUS uses UDP, not TCP. Option D is wrong because TACACS+ encrypts the entire packet body, not just the password.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
TACACS+ encrypts the entire packet body, whereas RADIUS only encrypts the password.
Why this is correct
Correct because TACACS+ encrypts the entire payload, while RADIUS only encrypts the password attribute.
- ✗
RADIUS uses TCP for reliable transport, while TACACS+ uses UDP.
Why it's wrong here
Incorrect because RADIUS uses UDP, and TACACS+ uses TCP.
- ✓
RADIUS combines authentication and authorization in one packet, whereas TACACS+ separates them.
Why this is correct
Correct because RADIUS typically combines AAA functions, while TACACS+ uses separate packets for each.
- ✗
TACACS+ encrypts only the password in the packet, similar to RADIUS.
Why it's wrong here
Incorrect because TACACS+ encrypts the entire packet body, not just the password.
- ✓
RADIUS uses UDP as its transport protocol, while TACACS+ uses TCP.
Why this is correct
Correct because RADIUS uses UDP (ports 1812/1813) and TACACS+ uses TCP (port 49).
Quick reference
AAA Protocol Comparison
| Protocol | Port(s) | Encryption | Transport | Primary Use |
|---|---|---|---|---|
| RADIUS | 1812 / 1813 | Password only | UDP | Network access control |
| TACACS+ | 49 | Full packet | TCP | Device administration |
| Diameter | 3868 | Full session | TCP / SCTP | Carrier / mobile networks |
| 802.1X | — | EAP-based | Layer 2 | Port-based access control |
TACACS+ encrypts the entire packet; RADIUS only encrypts the password field — a key exam distinction.
Go deeper
Related to this question
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VLANs and Spanning Tree Protocol Concepts
Key term
802.1X Authentication
802.1X is a network access control protocol that prevents unauthorized devices from connecting to a wired or wireless network by requiring them to authenticate before gaining access.
Key term
RADIUS vs TACACS+
RADIUS and TACACS+ are two network protocols used to verify user identities and control access to network devices and services, with different approaches to security and flexibility.
About these practice questions
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Same concept, more angles
1 more way this is tested on 350-401
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which three statements about RADIUS and TACACS+ are true? (Choose three.)
hard- ✓ A.RADIUS combines authentication and authorization in a single packet.
- ✓ B.TACACS+ uses TCP port 49 by default.
- C.RADIUS encrypts the entire packet payload for all attributes.
- ✓ D.TACACS+ provides separate authentication, authorization, and accounting processes.
- E.RADIUS supports per-command authorization for shell sessions.
Why A: RADIUS and TACACS+ are both AAA protocols but differ in transport, encryption, and authorization granularity. RADIUS uses UDP and encrypts only the password; TACACS+ uses TCP and encrypts the entire packet. TACACS+ supports per-command authorization, while RADIUS does not. Both can be used for device administration, but RADIUS is more common for network access.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.