- A
The implicit deny at the end of ACL 10 is blocking all outbound traffic from the 192.168.2.0/24 network.
Why wrong: Standard ACLs applied inbound on an interface only affect packets entering the router on that interface. Packets leaving G0/0 are not checked by this ACL, so outbound traffic from 192.168.2.0/24 is unaffected.
- B
The ACL is filtering return traffic from the Internet that enters G0/0, because it is applied inbound on that interface instead of outbound.
Inbound ACLs on G0/0 inspect packets arriving from the Internet. The ACL permits only source 192.168.1.0/24, so return packets from Internet hosts with random source IPs are denied by the implicit deny, breaking connectivity for 192.168.2.0/24 hosts.
- C
The router is not performing inter-VLAN routing between the 192.168.1.0 and 192.168.2.0 networks.
Why wrong: Inter-VLAN routing relies on the routing table, not ACLs, to forward packets between directly connected subnets. The ACL only filters traffic passing through the interface where it is applied and does not disable routing between the two LANs.
- D
The ACL is missing a permit statement for the 192.168.2.0/24 network to allow traffic from that subnet.
Why wrong: Even if a permit for 192.168.2.0/24 were added, the ACL is applied inbound on G0/0. Traffic from 192.168.2.0/24 going to the Internet would exit out G0/0, not enter, so it would not be evaluated by this ACL. The missing permit is not the root cause; the direction is wrong.
Quick Answer
The answer is that the ACL is filtering return traffic from the Internet because it is applied inbound on the wrong interface. When an ACL is applied inbound on GigabitEthernet0/0, it inspects packets as they enter the router through that interface—meaning it evaluates traffic coming from the Internet toward the router, not traffic leaving the LAN. Since ACL 10 only permits source addresses from 192.168.1.0/24, any return traffic from the Internet destined for the 192.168.2.0/24 hosts is denied by the implicit deny, breaking connectivity. This question tests your understanding of ACL direction impact on traffic filtering, a common CCNA 200-301 v2 trap where candidates confuse inbound versus outbound placement. The key is to visualize the data flow: an inbound ACL on G0/0 filters what comes in from the Internet, not what goes out to it. Memory tip: “Inbound inspects incoming, outbound oversees outgoing”—always match the ACL direction to the traffic you want to filter.
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.
A network engineer notices that hosts in the 192.168.2.0/24 network connected to router R1's GigabitEthernet0/1 interface cannot reach the Internet. R1 has a standard ACL 10 configured as 'access-list 10 permit 192.168.1.0 0.0.0.255' and applied inbound on interface GigabitEthernet0/0, which connects to the 192.168.1.0/24 LAN. 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.
Answer choices
Why each option matters
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 filtering return traffic from the Internet that enters G0/0, because it is applied inbound on that interface instead of outbound.
The ACL 10 is applied inbound on the G0/0 interface that faces the 192.168.1.0/24 LAN and the Internet. Inbound ACLs on that interface examine packets entering the router on G0/0, such as return traffic from the Internet. Since the ACL permits only source IPs from 192.168.1.0/24, all return traffic from the Internet destined for 192.168.2.0/24 hosts is denied by the implicit deny. This blocks replies, preventing connectivity. The ACL direction is incorrect for filtering egress traffic; an outbound ACL would be needed to filter packets leaving G0/0, and even then the source would still be denied unless explicitly permitted.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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 implicit deny at the end of ACL 10 is blocking all outbound traffic from the 192.168.2.0/24 network.
Why it's wrong here
Standard ACLs applied inbound on an interface only affect packets entering the router on that interface. Packets leaving G0/0 are not checked by this ACL, so outbound traffic from 192.168.2.0/24 is unaffected.
- ✓
The ACL is filtering return traffic from the Internet that enters G0/0, because it is applied inbound on that interface instead of outbound.
Why this is correct
Inbound ACLs on G0/0 inspect packets arriving from the Internet. The ACL permits only source 192.168.1.0/24, so return packets from Internet hosts with random source IPs are denied by the implicit deny, breaking connectivity for 192.168.2.0/24 hosts.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
- ✗
The router is not performing inter-VLAN routing between the 192.168.1.0 and 192.168.2.0 networks.
- ✗
The ACL is missing a permit statement for the 192.168.2.0/24 network to allow traffic from that subnet.
Why it's wrong here
Even if a permit for 192.168.2.0/24 were added, the ACL is applied inbound on G0/0. Traffic from 192.168.2.0/24 going to the Internet would exit out G0/0, not enter, so it would not be evaluated by this ACL. The missing permit is not the root cause; the direction is wrong.
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 filtering return traffic from the Internet that enters G0/0, because it is applied inbound on that interface instead of outbound.Correct answer▾
Why this is correct
Inbound ACLs on G0/0 inspect packets arriving from the Internet. The ACL permits only source 192.168.1.0/24, so return packets from Internet hosts with random source IPs are denied by the implicit deny, breaking connectivity for 192.168.2.0/24 hosts.
✗The implicit deny at the end of ACL 10 is blocking all outbound traffic from the 192.168.2.0/24 network.Wrong answer — click to see why▾
Why this is wrong here
Misunderstanding of ACL direction leads candidates to think that the implicit deny blocks any traffic leaving the interface.
✗The router is not performing inter-VLAN routing between the 192.168.1.0 and 192.168.2.0 networks.Wrong answer — click to see why▾
Why this is wrong here
Confusing ACL filtering with routing functionality; ACLs do not prevent the router from routing between connected subnets unless they explicitly deny the traffic on the appropriate interface and direction.
✗The ACL is missing a permit statement for the 192.168.2.0/24 network to allow traffic from that subnet.Wrong answer — click to see why▾
Why this is wrong here
Candidates often try to add a permit for the source subnet of the initiating traffic, neglecting the direction of the ACL. Because the ACL is inbound on the egress interface, outbound traffic is not filtered.
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: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
- Access ports place end devices into a single VLAN.
- Trunk ports carry multiple VLANs between switches.
- Allowed VLAN lists decide which VLANs can cross a trunk.
- Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
- Use show vlan brief to verify access VLANs.
- Use show interfaces trunk to verify trunk state and allowed VLANs.
- Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
Got this wrong? Here's your next step.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
- →
Network Services and Security — study guide chapter
Learn the concepts, then practise the questions
- →
Network Services and Security practice questions
Targeted practice on this topic area only
- →
All 200-301 questions
1,819 questions across all exam domains
- →
CCNA 200-301 v2 study guide
Full concept coverage aligned to exam objectives
- →
200-301 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related 200-301 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Network Infrastructure and Connectivity practice questions
Practise 200-301 questions linked to Network Infrastructure and Connectivity.
Switching and Network Access practice questions
Practise 200-301 questions linked to Switching and Network Access.
IP Routing practice questions
Practise 200-301 questions linked to IP Routing.
Network Services and Security practice questions
Practise 200-301 questions linked to Network Services and Security.
AI and Network Operations practice questions
Practise 200-301 questions linked to AI and Network Operations.
CCNA subnetting practice questions
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
CCNA OSPF practice questions
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
CCNA VLAN practice questions
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
CCNA STP practice questions
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
CCNA EtherChannel practice questions
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
CCNA ACL practice questions
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
CCNA NAT practice questions
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
Practice this exam
Start a free 200-301 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this 200-301 question test?
Network Services and Security — This question tests Network Services and Security — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The ACL is filtering return traffic from the Internet that enters G0/0, because it is applied inbound on that interface instead of outbound. — The ACL 10 is applied inbound on the G0/0 interface that faces the 192.168.1.0/24 LAN and the Internet. Inbound ACLs on that interface examine packets entering the router on G0/0, such as return traffic from the Internet. Since the ACL permits only source IPs from 192.168.1.0/24, all return traffic from the Internet destined for 192.168.2.0/24 hosts is denied by the implicit deny. This blocks replies, preventing connectivity. The ACL direction is incorrect for filtering egress traffic; an outbound ACL would be needed to filter packets leaving G0/0, and even then the source would still be denied unless explicitly permitted.
What should I do if I get this 200-301 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
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?
Access ports place end devices into a single VLAN.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Keep practising
More 200-301 practice questions
- A switchport connected to another switch should carry multiple VLANs, but it was manually configured as an access port.…
- What problem is HSRP designed to solve?
- Which TWO statements correctly describe the causes or implications of CRC errors, runts, giants, or output errors as see…
- You are connected to R1. Configure IPv4 and IPv6 addressing on R1's interfaces and verify reachability to R2. The curren…
- Which TWO statements accurately describe how AI/ML concepts are applied to network operations in modern enterprise netwo…
- Which TWO switch port configurations are required when connecting a Cisco IP phone and a desktop PC to a single access p…
Last reviewed: Jun 14, 2026
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.