hardMultiple Select
RADIUS vs TACACS+ Differences
Which three statements about RADIUS and TACACS+ are true? (Choose three.)
⚠ Common exam trap
The trap here is assuming RADIUS encrypts all data or supports command authorization like TACACS+; candidates often mix up the capabilities of the two protocols.
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
✓
RADIUS combines authentication and authorization in a single packet.
Option A is correct because RADIUS, defined in RFC 2865/2866, performs authentication and authorization together in a single Access-Request/Access-Accept exchange, so the two functions are not separated into distinct transactions. Option B is correct because TACACS+ operates over TCP and listens on port 49 by default, providing reliable transport unlike RADIUS's use of UDP. Option D is correct because TACACS+ is designed with fully separated AAA functions, allowing authentication, authorization, and accounting to be handled as independent processes and even directed to different servers. Option C is incorrect because RADIUS only encrypts the password (User-Password attribute) using a shared secret and MD5, leaving the rest of the packet payload, such as other attributes, in cleartext. Option E is incorrect because per-command authorization for shell/CLI sessions is a hallmark of TACACS+, whereas RADIUS lacks native support for granular per-command authorization.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
RADIUS combines authentication and authorization in a single packet.
Why this is correct
RADIUS merges authentication and authorization into one Access-Accept packet, returning attributes such as service type and IP assignment together. TACACS+ separates these functions, issuing distinct authentication and authorization exchanges. This combined-packet behaviour is the specific RADIUS trait being verified.
- ✓
TACACS+ uses TCP port 49 by default.
Why this is correct
TACACS+ uniquely transports authentication, authorisation and accounting over TCP port 49, giving reliable, connection-oriented delivery. RADIUS instead uses UDP ports 1812/1813, so this statement correctly distinguishes the two protocols and satisfies the stem's requirement for a true TACACS+ characteristic.
- ✗
RADIUS encrypts the entire packet payload for all attributes.
Why it's wrong here
RADIUS encrypts only the password field in Access-Request packets, using the shared secret; remaining attributes travel in cleartext. TACACS+ encrypts the whole packet body. The option would be correct if it described TACACS+, which protects all attribute payloads, not RADIUS.
- ✓
TACACS+ provides separate authentication, authorization, and accounting processes.
Why this is correct
TACACS+ separates authentication, authorization, and accounting into distinct processes, allowing granular control over each function independently. This contrasts with RADIUS, which combines authentication and authorization. The stem asks for true statements about the two protocols, and this accurately describes TACACS+'s defining architectural characteristic.
- ✗
RADIUS supports per-command authorization for shell sessions.
Why it's wrong here
RADIUS carries no per-command authorisation fields; its authorisation model is profile-based, returning attributes such as VLAN or ACL after authentication. TACACS+ separates authentication, authorisation and accounting, letting each shell command be permitted or denied. Per-command control is therefore a TACACS+ capability, and the option would be true only of that protocol.
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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Network Access Control and AAA
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.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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.