This 300-410 practice question tests your understanding of ipv4 access control lists. 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 engineer runs the following command to troubleshoot an IPv4 Access Control Lists issue:
R1# show ip access-lists 160
Extended IP access list 160
10 permit tcp 10.0.0.0 0.255.255.255 any eq 22
20 permit tcp 172.16.0.0 0.15.255.255 any eq 22
30 permit tcp 192.168.0.0 0.0.255.255 any eq 22
40 deny ip any anyWhat does this output indicate?
The ACL permits SSH from private IP ranges and denies all other traffic.
The entries permit SSH from the specified ranges and deny everything else.
The ACL permits all traffic from private IP ranges.
Why wrong: Only SSH is permitted.
The ACL denies SSH from private IP ranges.
Why wrong: SSH is permitted.
The ACL is applied inbound on an interface and is blocking all traffic.
Why wrong: It permits SSH from private ranges.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The ACL permits SSH from private IP ranges and denies all other traffic.
The ACL permits TCP traffic to destination port 22 (SSH) from the three private IP ranges (10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16) using wildcard masks that match the respective network prefixes. The final explicit deny ip any any statement blocks all other traffic, so only SSH from private IP ranges is permitted.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The ACL permits SSH from private IP ranges and denies all other traffic.
Why this is correct
The entries permit SSH from the specified ranges and deny everything else.
Related concept
Read the scenario before looking for a memorised answer.
The ACL permits all traffic from private IP ranges.
Why it's wrong here
Only SSH is permitted.
The ACL denies SSH from private IP ranges.
Why it's wrong here
SSH is permitted.
The ACL is applied inbound on an interface and is blocking all traffic.
Why it's wrong here
It permits SSH from private ranges.
Common exam traps
Cisco often tests the distinction between 'permit all traffic' and 'permit specific traffic (e.g., SSH only)', leading candidates to overlook the port-specific 'eq 22' and incorrectly assume the ACL permits all traffic from the private ranges.
Detailed technical explanation
The wildcard masks in this ACL are inverse masks: 0.255.255.255 matches the first octet exactly (10), 0.15.255.255 matches the first two octets with a 4-bit wildcard for the second octet (172.16.0.0–172.31.255.255), and 0.0.255.255 matches the first two octets exactly (192.168). The 'eq 22' matches only TCP destination port 22 (SSH), not source port, and the implicit deny at the end is made explicit by line 40, which is a best practice for visibility.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
IPv4 Access Control Lists — This question tests IPv4 Access Control Lists — Read the scenario before looking for a memorised answer..
The correct answer is: The ACL permits SSH from private IP ranges and denies all other traffic. — The ACL permits TCP traffic to destination port 22 (SSH) from the three private IP ranges (10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16) using wildcard masks that match the respective network prefixes. The final explicit deny ip any any statement blocks all other traffic, so only SSH from private IP ranges is permitted.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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