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Question 587 of 1,052
hardmultiple choiceObjective-mapped
CCNA Practice Question: Is troubleshooting connectivity issues on a router
This 200-301 practice question tests your understanding of is troubleshooting connectivity issues on a router. 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
interface GigabitEthernet0/0 ip address 192.168.1.1 255.255.255.0 duplex auto speed auto ! interface GigabitEthernet0/1.10 encapsulation dot1Q 10 ip address 192.168.10.1 255.255.255.0 ! interface GigabitEthernet0/1.20 encapsulation dot1Q 20 ip address 192.168.20.1 255.255.255.0 ! interface GigabitEthernet0/2 ip address 10.0.0.1 255.255.255.0 ip access-group OUTBOUND_FILTER out ! access-list 100 permit ip 192.168.10.0 0.0.0.255 192.168.20.0 0.0.0.255 access-list 100 permit ip 192.168.20.0 0.0.0.255 192.168.10.0 0.0.0.255 ! ip access-list extended OUTBOUND_FILTER permit tcp any any established deny ip any any ! ip route 0.0.0.0 0.0.0.0 10.0.0.2
A network engineer is troubleshooting connectivity issues on a router. Hosts on VLAN 10 (192.168.10.0/24) cannot ping hosts on VLAN 20 (192.168.20.0/24), though both VLANs are directly connected to the same router. The router's running configuration is shown. What is the most likely cause of the problem?
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
✓
Modify the OUTBOUND_FILTER ACL to permit ICMP traffic (e.g., permit icmp any any).
The ACL named OUTBOUND_FILTER is applied outbound on GigabitEthernet0/2, which is the interface facing the upstream router. This ACL only permits TCP traffic with the ACK or RST bit set (i.e., established connections) and denies all other IP traffic. Since ICMP (ping) is not TCP, the echo requests and replies are denied. The correct solution is to modify the ACL to permit ICMP or remove the ACL from that interface. The other options do not address the root cause: there is no inbound ACL on the subinterfaces, the ACL on GigabitEthernet0/2 is outbound, not inbound, and the ACL syntax is correct for established connections.
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.
- ✗
Add an inbound ACL on GigabitEthernet0/1.10 to permit traffic from VLAN 10 to VLAN 20.
Why it's wrong here
There is no ACL currently applied inbound on the subinterfaces, so adding one would not fix the issue and might cause further problems.
- ✓
Modify the OUTBOUND_FILTER ACL to permit ICMP traffic (e.g., permit icmp any any).
Why this is correct
The ACL currently only permits established TCP connections, so ICMP is denied. By adding a permit icmp statement, ping traffic will be allowed out the interface.
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.
- ✗
Change the direction of the ACL on GigabitEthernet0/2 from outbound to inbound.
Why it's wrong here
Changing the direction would cause the ACL to filter traffic entering the router from the upstream network, which is not the cause of the problem.
- ✗
Remove the 'established' keyword from the OUTBOUND_FILTER ACL.
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.
✓Modify the OUTBOUND_FILTER ACL to permit ICMP traffic (e.g., permit icmp any any).Correct answer▾
Why this is correct
The ACL currently only permits established TCP connections, so ICMP is denied. By adding a permit icmp statement, ping traffic will be allowed out the interface.
✗Add an inbound ACL on GigabitEthernet0/1.10 to permit traffic from VLAN 10 to VLAN 20.Wrong answer — click to see why▾
Why this is wrong here
The problem is not on the subinterface; it is the outbound ACL on GigabitEthernet0/2 that is blocking ICMP.
✗Change the direction of the ACL on GigabitEthernet0/2 from outbound to inbound.Wrong answer — click to see why▾
Why this is wrong here
The traffic from VLAN 10 to VLAN 20 does not traverse GigabitEthernet0/2 as incoming traffic; it exits via that interface only if destined to the upstream network, but the ping is between local VLANs.
✗Remove the 'established' keyword from the OUTBOUND_FILTER ACL.Wrong answer — click to see why▾
Why this is wrong here
ICMP is still not permitted, so ping would still fail.
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.
Trap categories for this question
Keyword trap
The 'established' keyword is correctly used to allow return traffic for TCP connections. Removing it would not help ICMP, which is not TCP.
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.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Access ports place end devices into a single VLAN.
What is the correct answer to this question?
The correct answer is: Modify the OUTBOUND_FILTER ACL to permit ICMP traffic (e.g., permit icmp any any). — The ACL named OUTBOUND_FILTER is applied outbound on GigabitEthernet0/2, which is the interface facing the upstream router. This ACL only permits TCP traffic with the ACK or RST bit set (i.e., established connections) and denies all other IP traffic. Since ICMP (ping) is not TCP, the echo requests and replies are denied. The correct solution is to modify the ACL to permit ICMP or remove the ACL from that interface. The other options do not address the root cause: there is no inbound ACL on the subinterfaces, the ACL on GigabitEthernet0/2 is outbound, not inbound, and the ACL syntax is correct for established connections.
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.
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