The correct answer is that the 'transport input ssh' command restricts the VTY line to accept only SSH connections, blocking Telnet. This is because the 'transport input' command on a VTY line explicitly defines which protocols are permitted for remote administration; when set to 'ssh', it denies all other protocols, including Telnet, which uses unencrypted traffic. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of secure device management and VTY line configuration, often appearing in questions about access control or security best practices. A common trap is confusing 'transport input ssh' with 'transport input telnet ssh', which allows both protocols—so remember that the command is exclusive, not additive. For a quick memory tip, think "SSH only, no Telnet—secure the line, don't forget it."
300-410 Device Access Control Practice Question
This 300-410 practice question tests your understanding of device access control. 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 of the following is true regarding the use of the 'transport input' command on a VTY line?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The 'transport input ssh' command allows only SSH connections, blocking Telnet.
Option B is correct because the 'transport input ssh' command explicitly restricts the VTY line to accept only SSH connections, blocking Telnet and other protocols. This is a common security best practice to ensure encrypted remote administration.
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.
✗
If 'transport input' is not configured, the VTY line defaults to allowing both Telnet and SSH.
The 'transport input ssh' command allows only SSH connections, blocking Telnet.
Why this is correct
This restricts the VTY to SSH only, enhancing security.
Related concept
Read the scenario before looking for a memorised answer.
✗
The 'transport input none' command allows all protocols.
Why it's wrong here
'transport input none' blocks all incoming connections.
✗
The 'transport input' command applies to both inbound and outbound VTY connections.
Why it's wrong here
It only affects inbound connections; outbound connections are controlled by 'transport output'.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the default behavior of 'transport input' — many candidates mistakenly believe it defaults to allowing both Telnet and SSH, but the actual default is to allow only Telnet (or 'all' on some platforms, but not both).
Trap categories for this question
Command / output trap
It only affects inbound connections; outbound connections are controlled by 'transport output'.
Detailed technical explanation
How to think about this question
The 'transport input' command controls which protocols are permitted for incoming sessions on a VTY line. When set to 'ssh', the line will reject Telnet (TCP port 23) and only accept SSH (TCP port 22). In contrast, 'transport output' controls outbound connections, and 'transport preferred' sets the default protocol for initiating connections. A common real-world scenario is securing management access by using 'transport input ssh' and optionally 'ip ssh version 2' to enforce modern encryption.
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 practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Device Access Control — This question tests Device Access Control — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The 'transport input ssh' command allows only SSH connections, blocking Telnet. — Option B is correct because the 'transport input ssh' command explicitly restricts the VTY line to accept only SSH connections, blocking Telnet and other protocols. This is a common security best practice to ensure encrypted remote administration.
What should I do if I get this 300-410 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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Question Discussion
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