- A
Generate a new RSA key pair and restart the SSH service.
Why wrong: SSH is already enabled and 'show ip ssh' confirms it is running. Generating a new key pair does not change the VTY transport configuration and would not resolve the 'connection refused' error.
- B
Add the 'transport input ssh' command to the VTY lines.
The show line vty output indicates only Telnet is permitted. Adding 'transport input ssh' (or 'transport input all') modifies the VTY configuration to accept both Telnet and SSH, directly fixing the protocol restriction causing the connection refused.
- C
Configure 'ip ssh version 1' to enable backward compatibility.
Why wrong: The router already runs SSH version 2, and version 1 is less secure and not required for compatibility. Changing the version does not override the VTY transport input restriction, so SSH connections will still be refused.
- D
Configure AAA authentication on the VTY lines.
Why wrong: AAA authentication is not required for SSH to function; the router is already using local authentication (implied by the working Telnet). The refusal occurs before authentication, at the transport protocol layer, so adding AAA would not resolve the issue.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
A network technician is troubleshooting a router that cannot be accessed via SSH. The router responds to Telnet but SSH attempts return 'connection refused'. The technician confirmed that 'ip ssh version 2' is configured and 'show ip ssh' indicates SSH is enabled. The output of 'show line vty 0 4' shows 'transport input telnet'. What should the technician do next?
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
Add the 'transport input ssh' command to the VTY lines.
The VTY lines are configured with 'transport input telnet', which explicitly allows only Telnet sessions. SSH is enabled globally, but because it is not listed in the VTY transport input, the router rejects SSH connection attempts. Adding 'transport input ssh' (or 'transport input all') under the VTY lines permits SSH connections without disrupting Telnet, solving the mismatch at the application layer.
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.
- ✗
Generate a new RSA key pair and restart the SSH service.
Why it's wrong here
SSH is already enabled and 'show ip ssh' confirms it is running. Generating a new key pair does not change the VTY transport configuration and would not resolve the 'connection refused' error.
- ✓
Add the 'transport input ssh' command to the VTY lines.
Why this is correct
The show line vty output indicates only Telnet is permitted. Adding 'transport input ssh' (or 'transport input all') modifies the VTY configuration to accept both Telnet and SSH, directly fixing the protocol restriction causing the connection refused.
Related concept
Authentication checks who the user is.
- ✗
Configure 'ip ssh version 1' to enable backward compatibility.
Why it's wrong here
The router already runs SSH version 2, and version 1 is less secure and not required for compatibility. Changing the version does not override the VTY transport input restriction, so SSH connections will still be refused.
- ✗
Configure AAA authentication on the VTY lines.
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.
✓Add the 'transport input ssh' command to the VTY lines.Correct answer▾
Why this is correct
The show line vty output indicates only Telnet is permitted. Adding 'transport input ssh' (or 'transport input all') modifies the VTY configuration to accept both Telnet and SSH, directly fixing the protocol restriction causing the connection refused.
✗Generate a new RSA key pair and restart the SSH service.Wrong answer — click to see why▾
Why this is wrong here
Administrators often mistake 'connection refused' for a key issue, but the VTY lines restrict the allowed protocols, not the validity of the keys.
✗Configure 'ip ssh version 1' to enable backward compatibility.Wrong answer — click to see why▾
Why this is wrong here
Candidates may think a version mismatch causes the refusal, but the VTY transport setting is the actual filter; downgrading security is unnecessary and ineffective.
✗Configure AAA authentication on the VTY lines.Wrong answer — click to see why▾
Why this is wrong here
Some technicians equate 'connection refused' with authentication failure and jump to AAA, but in this case the VTY lines never allow the SSH session to reach the authentication stage.
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: 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.
Trap categories for this question
Command / output trap
SSH is already enabled and 'show ip ssh' confirms it is running. Generating a new key pair does not change the VTY transport configuration and would not resolve the 'connection refused' error.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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 200-301 questions on access control and AAA configuration.
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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 — Authentication checks who the user is..
What is the correct answer to this question?
The correct answer is: Add the 'transport input ssh' command to the VTY lines. — The VTY lines are configured with 'transport input telnet', which explicitly allows only Telnet sessions. SSH is enabled globally, but because it is not listed in the VTY transport input, the router rejects SSH connection attempts. Adding 'transport input ssh' (or 'transport input all') under the VTY lines permits SSH connections without disrupting Telnet, solving the mismatch at the application layer.
What should I do if I get this 200-301 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 200-301 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 14, 2026
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