- A
RADIUS encrypts the entire packet payload, including all attributes.
Why wrong: RADIUS only encrypts the password attribute in the access-request packet; the rest of the packet is sent in clear text.
- B
TACACS+ encrypts the entire body of the packet but leaves the standard TCP header unencrypted.
TACACS+ encrypts the entire payload (body) of the packet, ensuring confidentiality of all attributes, while the TCP header remains unencrypted for routing purposes.
- C
TACACS+ uses UDP as its transport protocol, while RADIUS uses TCP.
Why wrong: In fact, RADIUS typically uses UDP (ports 1812/1813), and TACACS+ uses TCP (port 49).
- D
TACACS+ separates authentication, authorization, and accounting into three distinct functions, allowing independent server configuration for each.
TACACS+ architecture separates AAA into three distinct services, which can be handled by different servers or enabled/disabled independently.
- E
RADIUS combines authentication and authorization into a single process, meaning an access-accept packet includes both authentication success and authorization attributes.
RADIUS merges authentication and authorization; the access-accept message conveys both that the user is authenticated and what services they are authorized to use.
- F
When configuring 802.1X on IOS-XE, the switch acts as the authentication server and validates client credentials locally.
Why wrong: In 802.1X, the switch acts as an authenticator (passing messages between the client and the authentication server), not as the authentication server itself.
Quick Answer
The correct answer includes three statements: TACACS+ encrypts the entire packet body, TACACS+ separates authentication, authorization, and accounting into three distinct functions, and RADIUS combines authentication and authorization into a single process. This distinction is rooted in how each protocol handles AAA—RADIUS uses UDP and only encrypts the password in the Access-Request packet, leaving the rest of the payload in cleartext, while TACACS+ uses TCP and encrypts the entire packet body except the TCP header. On the CCNA 200-301 v2 exam, this topic tests your ability to compare RADIUS and TACACS+ for AAA authentication on Cisco IOS-XE, often appearing in multiple-choice questions where common traps include confusing encryption scopes or transport protocols. Remember that RADIUS is like a postcard—only the password is sealed—while TACACS+ is like a locked briefcase. For a quick memory tip: TACACS+ uses TCP (Think TCP for Total encryption), and RADIUS uses UDP (Unencrypted Data, mostly).
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 THREE statements correctly describe the configuration of AAA with RADIUS or TACACS+ on Cisco IOS-XE?
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 body of the packet but leaves the standard TCP header unencrypted.
Option B is correct: TACACS+ encrypts the entire body of the packet (including all attributes) but leaves the TCP header unencrypted. Option D is correct: TACACS+ separates authentication, authorization, and accounting into three distinct functions, allowing independent server configuration for each. Option E is correct: RADIUS combines authentication and authorization into a single process, so an access-accept packet includes both authentication success and authorization attributes. Option A is wrong: RADIUS only encrypts the password in the Access-Request packet, not the entire payload. Option C is wrong: TACACS+ uses TCP (port 49), while RADIUS uses UDP (ports 1812/1645 for authentication, 1813/1646 for accounting). Option F is wrong: In 802.1X on IOS-XE, the switch acts as an authenticator (not the authentication server) and forwards credentials to an external RADIUS server.
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 payload, including all attributes.
- ✓
TACACS+ encrypts the entire body of the packet but leaves the standard TCP header unencrypted.
- ✗
TACACS+ uses UDP as its transport protocol, while RADIUS uses TCP.
- ✓
TACACS+ separates authentication, authorization, and accounting into three distinct functions, allowing independent server configuration for each.
- ✓
RADIUS combines authentication and authorization into a single process, meaning an access-accept packet includes both authentication success and authorization attributes.
Why this is correct
RADIUS merges authentication and authorization; the access-accept message conveys both that the user is authenticated and what services they are authorized to use.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
When configuring 802.1X on IOS-XE, the switch acts as the authentication server and validates client credentials locally.
Why it's wrong here
In 802.1X, the switch acts as an authenticator (passing messages between the client and the authentication server), not as the authentication server itself.
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+ encrypts the entire body of the packet but leaves the standard TCP header unencrypted.Correct answer▾
Why this is correct
TACACS+ encrypts the entire payload (body) of the packet, ensuring confidentiality of all attributes, while the TCP header remains unencrypted for routing purposes.
✗RADIUS encrypts the entire packet payload, including all attributes.Wrong answer — click to see why▾
Why this is wrong here
RADIUS only encrypts the password attribute in the access-request packet; the rest of the packet, including other attributes like username and authorization data, is sent in clear text. This is a key security limitation of RADIUS compared to TACACS+.
Why candidates choose this
Students may confuse RADIUS's encryption of the password with full payload encryption, especially since RADIUS is often described as 'secure' in authentication contexts.
✗TACACS+ uses UDP as its transport protocol, while RADIUS uses TCP.Wrong answer — click to see why▾
Why this is wrong here
TACACS+ uses TCP (port 49) as its transport protocol, while RADIUS uses UDP (ports 1812/1813). This is a fundamental difference: TCP provides reliable, connection-oriented delivery, whereas UDP is connectionless and faster but less reliable.
Why candidates choose this
The names 'RADIUS' and 'TACACS+' are often confused, and students may incorrectly associate the more reliable protocol (TCP) with the more common protocol (RADIUS) or vice versa.
✗When configuring 802.1X on IOS-XE, the switch acts as the authentication server and validates client credentials locally.Wrong answer — click to see why▾
Why this is wrong here
In 802.1X, the switch acts as an authenticator (passing EAP messages between the client and the authentication server), not as the authentication server itself. The authentication server is typically a RADIUS server that validates client credentials.
Why candidates choose this
Students may think the switch performs local authentication because it is the device enforcing access control, but 802.1X relies on a separate authentication server for credential validation.
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 confusion between RADIUS and TACACS+ encryption scope and transport protocols, where candidates mistakenly think RADIUS encrypts the entire payload or that TACACS+ uses UDP, when in fact RADIUS only encrypts the password and uses UDP, while TACACS+ encrypts the full body and uses TCP.
Detailed technical explanation
How to think about this question
Under the hood, RADIUS uses a shared secret and MD5-based obfuscation only for the User-Password attribute, leaving the rest of the packet (including attributes like Framed-IP-Address or Vendor-Specific) unencrypted. TACACS+ separates authentication, authorization, and accounting into distinct phases, encrypting the entire body of each packet with a session key derived from a shared secret, while the TCP header remains in cleartext for routing. In real-world scenarios, this makes TACACS+ more suitable for environments requiring granular command authorization (e.g., Cisco device administration), whereas RADIUS is preferred for network access control (e.g., 802.1X wireless) where UDP's statelessness is acceptable.
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.
What to study next
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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+ encrypts the entire body of the packet but leaves the standard TCP header unencrypted. — Option B is correct: TACACS+ encrypts the entire body of the packet (including all attributes) but leaves the TCP header unencrypted. Option D is correct: TACACS+ separates authentication, authorization, and accounting into three distinct functions, allowing independent server configuration for each. Option E is correct: RADIUS combines authentication and authorization into a single process, so an access-accept packet includes both authentication success and authorization attributes. Option A is wrong: RADIUS only encrypts the password in the Access-Request packet, not the entire payload. Option C is wrong: TACACS+ uses TCP (port 49), while RADIUS uses UDP (ports 1812/1645 for authentication, 1813/1646 for accounting). Option F is wrong: In 802.1X on IOS-XE, the switch acts as an authenticator (not the authentication server) and forwards credentials to an external RADIUS server.
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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