- A
RADIUS encrypts the entire packet body, while TACACS+ encrypts only the password.
Why wrong: This statement is reversed: RADIUS encrypts only the password, while TACACS+ encrypts the entire packet body (except the header).
- B
TACACS+ uses TCP port 49, while RADIUS uses UDP ports 1812 and 1813.
TACACS+ uses TCP for reliable transport on port 49, while RADIUS uses UDP (port 1812 for authentication/authorization, 1813 for accounting).
- C
RADIUS supports command-level authorization, whereas TACACS+ does not.
Why wrong: TACACS+ supports per-command authorization (via the 'aaa authorization commands' feature), while RADIUS does not have native command-level authorization.
- D
TACACS+ separates authentication, authorization, and accounting into distinct processes, while RADIUS combines authentication and authorization.
TACACS+ uses separate AAA processes (each with its own packet type), allowing granular control. RADIUS combines authentication and authorization in the same Access-Request/Access-Accept exchange.
- E
Both RADIUS and TACACS+ can be used for 802.1X port-based authentication on IOS-XE.
Why wrong: Both RADIUS and TACACS+ can serve as AAA servers for 802.1X authentication on IOS-XE switches. However, RADIUS is more commonly used with 802.1X because of its native support for EAP.
RADIUS vs TACACS+: Protocol Differences for AAA Configuration
This 200-301 practice question tests your understanding of network services and security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which TWO statements correctly describe the differences between RADIUS and TACACS+ when configuring AAA on IOS-XE?
Quick Answer
The answer is that TACACS+ separates authentication, authorization, and accounting into distinct processes, while RADIUS combines authentication and authorization. This distinction stems from their architectural designs: TACACS+ uses TCP port 49 and encrypts the entire packet body, allowing granular control over each AAA function, whereas RADIUS uses UDP ports 1812 and 1813, encrypting only the password and bundling authentication with authorization. On the CCNA 200-301 v2 exam, this question tests your ability to differentiate protocol behaviors for AAA configuration on IOS-XE, often appearing as a multiple-select trap where you must avoid confusing encryption scope or port usage. A common pitfall is assuming RADIUS supports command-level authorization, which only TACACS+ does, or that 802.1X uses TACACS+ when it actually relies on RADIUS. Remember the mnemonic: “TACACS+ is Three separate processes, TCP, and Total body encryption; RADIUS is a Reduced service, UDP, and only the password is hidden.”
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+ uses TCP port 49, while RADIUS uses UDP ports 1812 and 1813.
Options B and D are correct. TACACS+ uses TCP port 49, while RADIUS uses UDP ports 1812 (authentication) and 1813 (accounting). TACACS+ separates authentication, authorization, and accounting into three distinct processes, whereas RADIUS combines authentication and authorization. Option A is incorrect because TACACS+ encrypts the entire packet body, while RADIUS encrypts only the password. Option C is incorrect because TACACS+ supports command-level authorization, while RADIUS does not. Option E is incorrect because 802.1X port-based authentication uses RADIUS, not TACACS+.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 encrypts the entire packet body, while TACACS+ encrypts only the password.
- ✓
TACACS+ uses TCP port 49, while RADIUS uses UDP ports 1812 and 1813.
- ✗
RADIUS supports command-level authorization, whereas TACACS+ does not.
- ✓
TACACS+ separates authentication, authorization, and accounting into distinct processes, while RADIUS combines authentication and authorization.
- ✗
Both RADIUS and TACACS+ can be used for 802.1X port-based authentication on IOS-XE.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓TACACS+ uses TCP port 49, while RADIUS uses UDP ports 1812 and 1813.Correct answer▾
Why this is correct
TACACS+ uses TCP for reliable transport on port 49, while RADIUS uses UDP (port 1812 for authentication/authorization, 1813 for accounting).
✗RADIUS encrypts the entire packet body, while TACACS+ encrypts only the password.Wrong answer — click to see why▾
Why this is wrong here
The encryption behavior is opposite to what is described.
✗RADIUS supports command-level authorization, whereas TACACS+ does not.Wrong answer — click to see why▾
Why this is wrong here
The statement reverses the capability: TACACS+ supports command authorization, not RADIUS.
✗Both RADIUS and TACACS+ can be used for 802.1X port-based authentication on IOS-XE.Wrong answer — click to see why▾
Why this is wrong here
Both RADIUS and TACACS+ can serve as AAA servers for 802.1X authentication on IOS-XE switches. However, RADIUS is more commonly used with 802.1X because of its native support for EAP.
★ When this WOULD be the correct answer
This is correct because both protocols are supported for 802.1X, though RADIUS is the typical choice.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the encryption behavior (Option A) as a trap, because candidates confuse which protocol encrypts the entire packet versus just the password, and they also test the authorization granularity (Option C) to see if you know that TACACS+ supports command-level authorization while RADIUS does not.
Trap categories for this question
Command / output trap
TACACS+ supports per-command authorization (via the 'aaa authorization commands' feature), while RADIUS does not have native command-level authorization.
Detailed technical explanation
How to think about this question
TACACS+ uses TCP to ensure reliable delivery of AAA packets, which is critical for command authorization where each command must be individually authorized. RADIUS uses UDP for lower overhead, making it suitable for high-volume authentication requests, but it lacks reliable delivery and requires retransmission logic at the application layer. In real-world deployments, TACACS+ is preferred for device administration (e.g., Cisco routers/switches) because of its granular command-level control, while RADIUS is commonly used for network access (e.g., VPN, wireless) due to its integration with attributes like VLAN assignment.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
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.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Network Services and Security — This question tests Network Services and Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: TACACS+ uses TCP port 49, while RADIUS uses UDP ports 1812 and 1813. — Options B and D are correct. TACACS+ uses TCP port 49, while RADIUS uses UDP ports 1812 (authentication) and 1813 (accounting). TACACS+ separates authentication, authorization, and accounting into three distinct processes, whereas RADIUS combines authentication and authorization. Option A is incorrect because TACACS+ encrypts the entire packet body, while RADIUS encrypts only the password. Option C is incorrect because TACACS+ supports command-level authorization, while RADIUS does not. Option E is incorrect because 802.1X port-based authentication uses RADIUS, not TACACS+.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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