The answer is that the traffic from host 10.1.1.100 is entering through a different interface than the one where the ACL is applied. ACLs filter traffic based on the specific interface and direction they are configured on; if the ACL is applied inbound on GigabitEthernet0/0 but the traffic reaches the router via GigabitEthernet0/1, the ACL never inspects that traffic, allowing it to pass freely. This question tests your understanding of ACL interface direction traffic different interface behavior, a core concept in the Cisco SCOR / CCNP Security Core 350-701 exam where misapplied ACLs are a common trap. Many candidates assume an ACL blocks all matching traffic globally, but Cisco IOS enforces filtering strictly at the interface level. Remember the memory tip: "ACLs are bouncers at a specific door—they don't check IDs at the back entrance."
350-701 Network Security Practice Question
This 350-701 practice question tests your understanding of network security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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
Refer to the exhibit.
ip access-list extended BLOCK_TRAFFIC
deny ip host 10.1.1.100 192.168.0.0 0.0.255.255
permit ip any any
!
interface GigabitEthernet0/0
ip access-group BLOCK_TRAFFIC in
An engineer applies the ACL shown in the exhibit to the inbound direction of interface GigabitEthernet0/0. The goal is to block all traffic from host 10.1.1.100 to the 192.168.0.0/16 network. However, traffic from 10.1.1.100 to 192.168.1.1 is still being permitted. 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.
Refer to the exhibit.
ip access-list extended BLOCK_TRAFFIC
deny ip host 10.1.1.100 192.168.0.0 0.0.255.255
permit ip any any
!
interface GigabitEthernet0/0
ip access-group BLOCK_TRAFFIC in
A
The deny entry should be placed after the permit entry
Why wrong: ACLs are processed top-down; the deny entry is first, so it should match before the permit.
B
The ACL should be applied outbound instead of inbound
Why wrong: Inbound ACL filters traffic coming into the interface; if the traffic arrives on that interface, inbound is correct.
C
The ACL is applied to the wrong direction; it should be 'out'
Why wrong: For blocking inbound traffic, the 'in' direction is correct.
D
The traffic from 10.1.1.100 is entering through a different interface
If the traffic does not enter via GigabitEthernet0/0, the ACL will not be applied to it.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The traffic from 10.1.1.100 is entering through a different interface
Option D is correct because ACLs process traffic only on the interface and direction to which they are applied. If the ACL is applied inbound on GigabitEthernet0/0 but the traffic from host 10.1.1.100 to 192.168.1.1 enters through a different interface (e.g., GigabitEthernet0/1), the ACL will never evaluate that traffic, allowing it to pass. This is a fundamental behavior of interface-based ACL filtering in Cisco IOS.
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 deny entry should be placed after the permit entry
Why it's wrong here
ACLs are processed top-down; the deny entry is first, so it should match before the permit.
✗
The ACL should be applied outbound instead of inbound
Why it's wrong here
Inbound ACL filters traffic coming into the interface; if the traffic arrives on that interface, inbound is correct.
✗
The ACL is applied to the wrong direction; it should be 'out'
Why it's wrong here
For blocking inbound traffic, the 'in' direction is correct.
✓
The traffic from 10.1.1.100 is entering through a different interface
Why this is correct
If the traffic does not enter via GigabitEthernet0/0, the ACL will not be applied to it.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume an ACL applied inbound on one interface will filter all traffic from a source, but Cisco tests the understanding that ACLs are interface- and direction-specific, and traffic can bypass the ACL if it enters through a different interface.
Detailed technical explanation
How to think about this question
Cisco ACLs are stateless packet filters that evaluate each packet against the ACEs in sequential order, and they only apply to traffic crossing the specific interface in the specified direction. In a multi-interface router, traffic from host 10.1.1.100 destined for 192.168.1.1 might enter via a different interface (e.g., a WAN interface) and be routed directly to the destination without ever being processed by the inbound ACL on GigabitEthernet0/0. This is a common misconfiguration in real-world scenarios where administrators assume a single ACL on one interface will protect all traffic, but it only filters traffic on that specific path.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The traffic from 10.1.1.100 is entering through a different interface — Option D is correct because ACLs process traffic only on the interface and direction to which they are applied. If the ACL is applied inbound on GigabitEthernet0/0 but the traffic from host 10.1.1.100 to 192.168.1.1 enters through a different interface (e.g., GigabitEthernet0/1), the ACL will never evaluate that traffic, allowing it to pass. This is a fundamental behavior of interface-based ACL filtering in Cisco IOS.
What should I do if I get this 350-701 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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