- A
The default UDP port for RADIUS authentication is 1812.
Correct because IANA assigned port 1812 for RADIUS authentication.
- B
The shared secret configured on the Cisco device must match the shared secret on the RADIUS server.
Correct because the shared secret is used to encrypt the password and must be identical on both sides.
- C
The 'radius-server host' command can include an optional 'key' parameter to specify the shared secret.
Correct because the command syntax allows specifying the key with the 'key' keyword.
- D
RADIUS uses TCP to ensure reliable delivery of authentication packets.
Why wrong: Incorrect because RADIUS uses UDP, not TCP; reliability is handled by retransmission timers.
- E
If no port is specified, RADIUS uses port 1645 for authentication by default.
Why wrong: Incorrect because the default port is 1812; port 1645 is an older, deprecated port.
Quick Answer
The correct answer includes the statement that the 'radius-server host' command can include an optional 'key' parameter to specify the shared secret. This is true because RADIUS server configuration on Cisco devices requires the IP address, the shared secret for mutual authentication, and the UDP ports—default authentication port 1812 and accounting port 1813—to be explicitly defined. On the ENCOR 350-401 exam, this topic tests your understanding of AAA deployment fundamentals, often appearing in multiple-choice questions that ask which three statements are true, with traps involving incorrect port numbers (like 1645) or the misconception that the shared secret is encrypted in transit. A common memory tip is to remember that RADIUS uses UDP and the shared secret is sent in cleartext within the packet, while only the password is MD5-hashed. For the exam, always verify that the shared secret matches on both the client and server, and that the key parameter is optional but recommended for security.
350-401 AAA, RADIUS, and TACACS+ Practice Question
This 350-401 practice question tests your understanding of aaa, radius, and tacacs+. 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 about RADIUS server configuration and operation are true? (Choose three.)
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
The default UDP port for RADIUS authentication is 1812.
RADIUS servers are configured with IP address, shared secret, and UDP ports. The default authentication port is 1812 and accounting port is 1813. The shared secret must match on both client and server. The 'radius-server host' command can specify the key. RADIUS uses MD5 for password encryption, but the shared secret is sent in cleartext within the packet.
Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The default UDP port for RADIUS authentication is 1812.
Why this is correct
Correct because IANA assigned port 1812 for RADIUS authentication.
Related concept
Authentication checks who the user is.
- ✓
The shared secret configured on the Cisco device must match the shared secret on the RADIUS server.
Why this is correct
Correct because the shared secret is used to encrypt the password and must be identical on both sides.
Related concept
Authentication checks who the user is.
- ✓
The 'radius-server host' command can include an optional 'key' parameter to specify the shared secret.
Why this is correct
Correct because the command syntax allows specifying the key with the 'key' keyword.
Related concept
Authentication checks who the user is.
- ✗
RADIUS uses TCP to ensure reliable delivery of authentication packets.
- ✗
If no port is specified, RADIUS uses port 1645 for authentication by default.
Why it's wrong here
Incorrect because the default port is 1812; port 1645 is an older, deprecated port.
Common exam traps
Common exam trap: authentication is not authorization
Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.
Detailed technical explanation
How to think about this question
This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.
KKey Concepts to Remember
- Authentication checks who the user is.
- Authorization controls what the user is allowed to do after login.
- Privilege levels affect access to EXEC and configuration commands.
- AAA, TACACS+ and RADIUS can separate login success from command access.
TExam Day Tips
- Do not assume successful login means full administrative access.
- Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
- Separate login problems from permission problems before choosing the answer.
Key takeaway
Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
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
Got this wrong? Here's your next step.
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related 350-401 questions on access control and AAA configuration.
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FAQ
Questions learners often ask
What does this 350-401 question test?
AAA, RADIUS, and TACACS+ — This question tests AAA, RADIUS, and TACACS+ — Authentication checks who the user is..
What is the correct answer to this question?
The correct answer is: The default UDP port for RADIUS authentication is 1812. — RADIUS servers are configured with IP address, shared secret, and UDP ports. The default authentication port is 1812 and accounting port is 1813. The shared secret must match on both client and server. The 'radius-server host' command can specify the key. RADIUS uses MD5 for password encryption, but the shared secret is sent in cleartext within the packet.
What should I do if I get this 350-401 question wrong?
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related 350-401 questions on access control and AAA configuration.
What is the key concept behind this question?
Authentication checks who the user is.
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Last reviewed: Jun 18, 2026
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