The answer is that the ACL entries are in the wrong order, with the deny statement placed before the permit statement. This is the most likely cause because Cisco ACLs are processed top-down in sequential order, and the first matching entry is applied immediately—so traffic from 192.168.10.0/24 to 192.168.20.0/24 matches the deny rule first and is dropped, even though a subsequent permit ip any any would have allowed it. On the CCNA 200-301 v2 exam, this scenario tests your understanding of ACL order and processing, a common trap where students assume a permit statement later in the list will override an earlier deny. The show ip access-lists output confirms the issue by showing higher match counters on the deny entry. For ACL order troubleshooting, always remember: first match wins, so place specific denies after your broad permits. A helpful memory tip is “Permit first, deny last—or your traffic won’t last.”
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.
Exhibit
R1# show ip access-lists
Extended IP access list 110
10 deny ip 192.168.10.0 0.0.0.255 192.168.20.0 0.0.0.255 (145 matches)
20 permit ip 192.168.10.0 0.0.0.255 any (95 matches)
Extended IP access list BLOCK_WEB
10 deny tcp any any eq 80
20 deny tcp any any eq 443
30 permit ip any any (5 matches)
Standard IP access list 10
10 permit 192.168.10.0 0.0.0.255 (21 matches)
20 deny any (8 matches)
Refer to the exhibit. A network administrator is troubleshooting connectivity issues. Hosts on the 192.168.10.0/24 network cannot reach servers on the 192.168.20.0/24 network, but they can successfully reach other networks, including the Internet. The administrator runs the show ip access-lists command on the router (output shown). What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
R1# show ip access-lists
Extended IP access list 110
10 deny ip 192.168.10.0 0.0.0.255 192.168.20.0 0.0.0.255 (145 matches)
20 permit ip 192.168.10.0 0.0.0.255 any (95 matches)
Extended IP access list BLOCK_WEB
10 deny tcp any any eq 80
20 deny tcp any any eq 443
30 permit ip any any (5 matches)
Standard IP access list 10
10 permit 192.168.10.0 0.0.0.255 (21 matches)
20 deny any (8 matches)
A
The ACL is applied in the wrong direction on the interface.
Why wrong: If the ACL were applied in the wrong direction, traffic from 192.168.10.0/24 to other networks would also be blocked, but the problem states that hosts can reach other networks. The output does not show interface application information, so direction is not indicated by the exhibit.
B
The ACL is missing a permit statement for the 192.168.20.0/24 destination.
Why wrong: The ACL has a permit ip any statement (entry 20) that would match traffic to 192.168.20.0/24 if it were evaluated before the deny. The missing permit is not the issue; the order causes the deny to match first.
C
The order of the ACL entries causes the deny statement to match first.
Extended IP access list 110 processes entries sequentially. Entry 10 denies traffic from 192.168.10.0/24 to 192.168.20.0/24, and entry 20 permits the same source to any destination. Because the deny is listed first, it is matched before the permit, causing the traffic to be dropped.
D
The implicit deny at the end is blocking the traffic to 192.168.20.0/24.
Why wrong: The implicit deny would only block traffic that does not match any explicit entry. Here, the traffic matches the explicit deny rule (entry 10), so the implicit deny is not reached. The hit counter on entry 10 confirms explicit matching.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The order of the ACL entries causes the deny statement to match first.
The exhibit shows Extended IP access list 110 with a deny statement for traffic from 192.168.10.0/24 to 192.168.20.0/24 (entry 10) placed before a permit ip any statement (entry 20). Because ACLs are processed in sequential order, the first matching entry is used. Traffic from 192.168.10.0/24 to 192.168.20.0/24 matches the deny statement and is dropped, even though a subsequent permit entry would allow it. The counters (145 matches for deny, 95 matches for permit) confirm that the deny is being hit first.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 applied in the wrong direction on the interface.
Why it's wrong here
If the ACL were applied in the wrong direction, traffic from 192.168.10.0/24 to other networks would also be blocked, but the problem states that hosts can reach other networks. The output does not show interface application information, so direction is not indicated by the exhibit.
✗
The ACL is missing a permit statement for the 192.168.20.0/24 destination.
Why it's wrong here
The ACL has a permit ip any statement (entry 20) that would match traffic to 192.168.20.0/24 if it were evaluated before the deny. The missing permit is not the issue; the order causes the deny to match first.
✓
The order of the ACL entries causes the deny statement to match first.
Why this is correct
Extended IP access list 110 processes entries sequentially. Entry 10 denies traffic from 192.168.10.0/24 to 192.168.20.0/24, and entry 20 permits the same source to any destination. Because the deny is listed first, it is matched before the permit, causing the traffic to be dropped.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The implicit deny at the end is blocking the traffic to 192.168.20.0/24.
Why it's wrong here
The implicit deny would only block traffic that does not match any explicit entry. Here, the traffic matches the explicit deny rule (entry 10), so the implicit deny is not reached. The hit counter on entry 10 confirms explicit matching.
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.
✓The order of the ACL entries causes the deny statement to match first.Correct answer▾
Why this is correct
Extended IP access list 110 processes entries sequentially. Entry 10 denies traffic from 192.168.10.0/24 to 192.168.20.0/24, and entry 20 permits the same source to any destination. Because the deny is listed first, it is matched before the permit, causing the traffic to be dropped.
✗The ACL is applied in the wrong direction on the interface.Wrong answer — click to see why▾
Why this is wrong here
Candidates may assume any ACL misbehavior is due to wrong interface direction, ignoring that the specific symptom (only 192.168.20.0 is unreachable) points to the deny rule itself.
✗The ACL is missing a permit statement for the 192.168.20.0/24 destination.Wrong answer — click to see why▾
Why this is wrong here
Candidates often focus on what an ACL ‘lacks’ rather than the sequence, missing that the existing permit any covers the destination but is shadowed by the earlier deny.
✗The implicit deny at the end is blocking the traffic to 192.168.20.0/24.Wrong answer — click to see why▾
Why this is wrong here
Candidates might recall that all ACLs have an implicit deny, but they fail to realize that a packet matching an earlier deny is already discarded, and the implicit deny only applies to unmatched traffic.
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: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Trap categories for this question
Command / output trap
If the ACL were applied in the wrong direction, traffic from 192.168.10.0/24 to other networks would also be blocked, but the problem states that hosts can reach other networks. The output does not show interface application information, so direction is not indicated by the exhibit.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 200-301 question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 200-301 NAT questions on configuration and troubleshooting.
Network Services and Security — This question tests Network Services and Security — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The order of the ACL entries causes the deny statement to match first. — The exhibit shows Extended IP access list 110 with a deny statement for traffic from 192.168.10.0/24 to 192.168.20.0/24 (entry 10) placed before a permit ip any statement (entry 20). Because ACLs are processed in sequential order, the first matching entry is used. Traffic from 192.168.10.0/24 to 192.168.20.0/24 matches the deny statement and is dropped, even though a subsequent permit entry would allow it. The counters (145 matches for deny, 95 matches for permit) confirm that the deny is being hit first.
What should I do if I get this 200-301 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 200-301 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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