Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
Exhibit
line vty 0 4 access-class 12 in transport input ssh access-list 12 permit 10.5.5.0 0.0.0.255
Exhibit: An engineer applies an ACL inbound on the VTY lines to permit SSH only from 10.5.5.0/24. Users from that subnet still cannot connect. What is the most likely reason?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
The device may not have SSH fully enabled with keys and a valid login method
The ACL allows the subnet, but SSH still needs its base configuration.
B
Distractor review
The ACL must be applied outbound on the VTY lines
Inbound is the correct direction for controlling management access to the device.
C
Distractor review
SSH requires UDP port 22
SSH uses TCP port 22.
D
Distractor review
VTY access-class can only be used with Telnet
It can absolutely be used with SSH.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is believing that simply applying an ACL to permit SSH traffic on the VTY lines guarantees remote access. Candidates often overlook that SSH requires full configuration, including RSA key generation, domain name setting, and valid login credentials. Without these, the device will refuse SSH connections regardless of ACL permissions. Another pitfall is misapplying the ACL outbound instead of inbound on VTY lines, which does not control incoming management sessions. Also, confusing SSH’s use of TCP port 22 with UDP can lead to incorrect ACL configurations. Recognizing these nuances prevents misinterpretation of the question and ensures correct troubleshooting.
Technical deep dive
How to think about this question
Access Control Lists (ACLs) are essential tools in Cisco networking to filter traffic based on IP addresses, protocols, and ports. When applied inbound on VTY lines, ACLs filter incoming management traffic before it reaches the device's virtual terminal interface, effectively controlling which hosts can attempt remote connections such as SSH or Telnet. However, ACLs only filter traffic; they do not enable or configure the management protocols themselves. SSH (Secure Shell) is a secure protocol used for remote management of Cisco devices. To allow SSH access, the device must have SSH fully enabled, which includes generating RSA key pairs, setting a domain name, and configuring valid login credentials such as local usernames or external authentication servers. The VTY lines must also be configured with 'transport input ssh' to accept only SSH connections. Without these configurations, even if an ACL permits SSH traffic from a subnet, the device will reject connection attempts. A common exam trap is assuming that applying an ACL to permit SSH traffic is sufficient for remote access. In reality, the device must be fully configured for SSH. Additionally, applying the ACL outbound on VTY lines is ineffective because inbound filtering controls access to the management interface. Understanding the distinction between enabling SSH and filtering SSH traffic is critical for both exam success and practical network security management.
KKey Concepts to Remember
- Access Control Lists (ACLs) applied inbound on VTY lines filter management traffic before it reaches the device's virtual terminal interface.
- SSH access to Cisco devices requires enabling SSH with RSA key generation, a domain name, and a valid local username and password or external authentication.
- The 'transport input ssh' command on VTY lines restricts remote management to SSH only, blocking Telnet or other protocols.
- ACLs control which IP addresses can initiate SSH sessions but do not enable SSH functionality by themselves.
- Without proper SSH configuration, including keys and login methods, ACLs permitting SSH traffic will not allow successful connections.
- Applying an ACL outbound on VTY lines is ineffective because inbound filtering controls access to the management interface.
- SSH uses TCP port 22, not UDP, so ACLs must permit TCP port 22 traffic for SSH connections.
- The 'access-class' command on VTY lines works with both Telnet and SSH to restrict remote access based on IP addresses.
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.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
Access Control Lists (ACLs) applied inbound on VTY lines filter management traffic before it reaches the device's virtual terminal interface.
What is the correct answer to this question?
The correct answer is: The device may not have SSH fully enabled with keys and a valid login method — Restricting the VTY lines is not enough if SSH itself has not been enabled correctly. A missing local username, domain name, RSA keys, or transport input ssh setting can stop access even when the ACL is correct.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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