300-410 IPv4 Access Control Lists Practice Question
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 101
Extended IP access list 101
10 permit tcp 192.168.1.0 0.0.0.255 any eq 80 (12 matches)
20 deny tcp any any eq 443 (5 matches)
30 permit ip any any (100 matches)
The ACL is permitting TCP traffic from 192.168.1.0/24 to any destination on port 80, denying all TCP traffic to port 443, and permitting all other IP traffic.
The ACL lines and match counts confirm this behavior.
B
The ACL is denying all traffic because line 20 is an explicit deny.
Why wrong: Line 30 permits all IP traffic, so not all traffic is denied.
C
The ACL is applied inbound on an interface and is blocking all traffic to port 443.
Why wrong: The ACL permits all other traffic, including to port 443 from 192.168.1.0/24? No, line 20 denies all TCP to port 443, but line 30 permits all IP, so TCP to 443 is denied.
D
The ACL has no effect because the match counts are too low.
Why wrong: Match counts are valid and show the ACL is being used.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The ACL is permitting TCP traffic from 192.168.1.0/24 to any destination on port 80, denying all TCP traffic to port 443, and permitting all other IP traffic.
Option A is correct because the ACL explicitly permits TCP traffic from source 192.168.1.0/24 to any destination on port 80 (line 10), denies TCP traffic from any source to any destination on port 443 (line 20), and then permits all other IP traffic (line 30). The match counts confirm that traffic matching each line has been processed, and the implicit deny at the end is never reached because line 30 permits everything else.
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.
✓
The ACL is permitting TCP traffic from 192.168.1.0/24 to any destination on port 80, denying all TCP traffic to port 443, and permitting all other IP traffic.
Why this is correct
The ACL lines and match counts confirm this behavior.
Related concept
Read the scenario before looking for a memorised answer.
✗
The ACL is denying all traffic because line 20 is an explicit deny.
Why it's wrong here
Line 30 permits all IP traffic, so not all traffic is denied.
✗
The ACL is applied inbound on an interface and is blocking all traffic to port 443.
Why it's wrong here
The ACL permits all other traffic, including to port 443 from 192.168.1.0/24? No, line 20 denies all TCP to port 443, but line 30 permits all IP, so TCP to 443 is denied.
✗
The ACL has no effect because the match counts are too low.
Why it's wrong here
Match counts are valid and show the ACL is being used.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that an explicit deny statement (like line 20) blocks all traffic, when in fact it only blocks the specific protocol and port, and subsequent permit entries can still allow other traffic.
Trap categories for this question
Command / output trap
Match counts are valid and show the ACL is being used.
Detailed technical explanation
How to think about this question
ACLs are processed top-down with an implicit deny ip any any at the end, but here line 30 explicitly permits all IP traffic, overriding that implicit deny. The match counters increment per packet that matches a given entry, and the 'any' keyword in line 30 matches all IP protocols (including TCP, UDP, ICMP, etc.), not just TCP. In real-world scenarios, such an ACL might be used to allow web traffic from a specific subnet while blocking HTTPS to enforce security policies, but the permit ip any any at the end could inadvertently allow other traffic that should be restricted.
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 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
IPv4 Access Control Lists — This question tests IPv4 Access Control Lists — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The ACL is permitting TCP traffic from 192.168.1.0/24 to any destination on port 80, denying all TCP traffic to port 443, and permitting all other IP traffic. — Option A is correct because the ACL explicitly permits TCP traffic from source 192.168.1.0/24 to any destination on port 80 (line 10), denies TCP traffic from any source to any destination on port 443 (line 20), and then permits all other IP traffic (line 30). The match counts confirm that traffic matching each line has been processed, and the implicit deny at the end is never reached because line 30 permits everything else.
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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