The answer is that the ACL is applied in the wrong place or direction for the traffic flow. Standard ACLs filter traffic based solely on the source IP address, so if users from 192.168.31.0/24 are still passing traffic despite the ACL permitting only 192.168.30.0/24, the filter is simply not positioned to inspect their packets. For the implicit deny to block them, the ACL must be applied inbound on the interface where their traffic enters the router, or outbound on the interface where it exits toward the destination. On the CCNA 200-301 v2 exam, this scenario tests your understanding that placement and direction are just as critical as the permit or deny statements themselves—a common trap is to focus only on the ACL logic while ignoring where it is actually enforced. Remember the memory tip: “Standard ACLs are source-blind to direction; if the traffic doesn’t cross the applied interface, the rule is just a decoration.”
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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
ip access-list standard USERS_ONLY
permit 192.168.30.0 0.0.0.255
deny any
interface g0/1
ip access-group USERS_ONLY out
A named standard ACL is configured to permit only the 192.168.30.0/24 subnet, but users from 192.168.31.0/24 are still passing traffic. What is the most likely reason?
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.
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 probably applied in the wrong place or direction for the traffic flow
Standard ACLs filter traffic based solely on the source IP address. If users from 192.168.31.0/24 are still passing traffic despite the ACL permitting only 192.168.30.0/24, the most likely reason is that the ACL is applied in the wrong place or direction. For example, if the ACL is applied inbound on an interface where traffic from 192.168.31.0/24 does not enter, or outbound on an interface where the traffic does not exit, the filter will not affect the intended flow. The implicit deny statement denies all unmatched traffic, so if the ACL were correctly placed, traffic from 192.168.31.0/24 would be denied.
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.
✗
Standard ACLs cannot match source addresses
Why it's wrong here
That is exactly what they match.
✓
The ACL is probably applied in the wrong place or direction for the traffic flow
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Named ACLs ignore wildcard masks
Why it's wrong here
They do not.
✗
The deny any line must appear before the permit
Why it's wrong here
That would block everything.
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 ACL is probably applied in the wrong place or direction for the traffic flowCorrect answer▾
Why this is correct
ACL placement matters a lot with standard ACLs.
✗Standard ACLs cannot match source addressesWrong answer — click to see why▾
Why this is wrong here
Standard ACLs are specifically designed to match source IP addresses, so this statement is factually incorrect. They can match source addresses using wildcard masks.
Why candidates choose this
Students might confuse standard ACLs with extended ACLs, thinking standard ACLs cannot match source addresses, but they actually can, though they lack the ability to match destination addresses or ports.
✗Named ACLs ignore wildcard masksWrong answer — click to see why▾
Why this is wrong here
Named ACLs use wildcard masks just like numbered ACLs; the naming does not affect the functionality of wildcard masks. The statement is technically incorrect.
Why candidates choose this
Students might think that named ACLs have different syntax or capabilities, but they are functionally identical to numbered ACLs except for the naming method.
✗The deny any line must appear before the permitWrong answer — click to see why▾
Why this is wrong here
The 'deny any' line at the end of an ACL is implicit, so placing it before the permit would block all traffic, including the intended 192.168.30.0/24 subnet. The order of entries matters, but the issue here is not about the order of deny any.
Why candidates choose this
Students often confuse the implicit deny any rule and think they need to explicitly add it, but the problem described is that traffic from 192.168.31.0/24 is passing, which would be denied by the implicit deny any if the ACL were correctly applied. The issue is placement, not the order of deny any.
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: answer the scenario, not the keyword
Remember that ACLs must be applied in the correct direction to affect traffic flow as intended.
Detailed technical explanation
How to think about this question
Standard ACLs (numbered 1-99 or 1300-1999, or named) evaluate packets sequentially from top to bottom, with an implicit deny all at the end. The wildcard mask in an ACL entry uses a 32-bit binary mask where 0 means 'must match' and 1 means 'ignore'; for 192.168.30.0/24, the correct wildcard mask is 0.0.0.255. In a real-world scenario, misapplying the ACL on the wrong interface (e.g., WAN instead of LAN) or wrong direction (inbound vs. outbound) is a common misconfiguration that leads to traffic bypassing the intended filter.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Network Services and Security — This question tests Network Services and Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The ACL is probably applied in the wrong place or direction for the traffic flow — Standard ACLs filter traffic based solely on the source IP address. If users from 192.168.31.0/24 are still passing traffic despite the ACL permitting only 192.168.30.0/24, the most likely reason is that the ACL is applied in the wrong place or direction. For example, if the ACL is applied inbound on an interface where traffic from 192.168.31.0/24 does not enter, or outbound on an interface where the traffic does not exit, the filter will not affect the intended flow. The implicit deny statement denies all unmatched traffic, so if the ACL were correctly placed, traffic from 192.168.31.0/24 would be denied.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
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