Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A switch trunk is carrying several VLANs, but VLAN 99 traffic is failing. The trunk allowed list includes VLAN 99 on both sides. Which statement best explains why a VLAN can still fail even when it is allowed?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
Because the VLAN may still be absent, inactive, or otherwise not operational locally even if it is allowed on the trunk
This is correct because an allowed-list entry alone does not guarantee that the VLAN exists and operates correctly end to end.
B
Distractor review
Because allowing a VLAN on a trunk automatically disables it
This is wrong because allowing a VLAN does not disable it.
C
Distractor review
Because VLANs can cross trunks only when PAT is enabled
This is wrong because PAT is unrelated to VLAN carriage on trunks.
D
Distractor review
Because VLAN 99 must always be the native VLAN
This is wrong because a VLAN does not have to be the native VLAN in order to work across a trunk.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is assuming that simply including VLAN 99 in the trunk allowed list guarantees that VLAN 99 traffic will pass. Many candidates stop troubleshooting once they see the VLAN is allowed on the trunk, neglecting to verify if VLAN 99 is actually created and active on each switch. This mistake leads to incorrect conclusions, as the allowed list only controls trunk forwarding permissions, not VLAN existence or operational status. The exam tests your understanding that VLAN configuration and status are equally critical for successful VLAN traffic flow.
Technical deep dive
How to think about this question
A VLAN (Virtual Local Area Network) logically segments a switched network into separate broadcast domains, allowing devices to communicate as if they were on distinct physical networks. Switch trunks carry traffic for multiple VLANs simultaneously by tagging frames with VLAN identifiers, typically using the IEEE 802.1Q standard. The trunk allowed VLAN list controls which VLANs are permitted to traverse the trunk link, but this list only governs frame forwarding on the trunk interface itself. Even if VLAN 99 is included in the trunk allowed list on both ends, the VLAN must also be defined and active locally on each switch. This means the VLAN must exist in the VLAN database, be operational (not shutdown), and have associated Layer 2 interfaces or ports assigned to it. If VLAN 99 is missing, inactive, or misconfigured on either switch, traffic for that VLAN will fail despite being allowed on the trunk. Thus, the allowed VLAN list is necessary but not sufficient for VLAN traffic to pass. A common exam trap is assuming that allowing a VLAN on a trunk automatically guarantees connectivity for that VLAN. Candidates often overlook the local VLAN configuration status and operational state. In practice, VLANs must be consistently configured and active on all switches in the path. Failure to verify VLAN presence and status can lead to troubleshooting delays and incorrect conclusions about trunk or VLAN issues.
KKey Concepts to Remember
- A VLAN must be locally defined and active on a switch for traffic to pass, even if it is allowed on the trunk link.
- The trunk allowed VLAN list controls which VLANs can traverse the trunk but does not create or activate VLANs on the switch.
- Switch trunks use 802.1Q tagging to carry multiple VLANs, requiring consistent VLAN configuration on both ends.
- Traffic for a VLAN fails if the VLAN is absent or inactive locally, regardless of trunk allowed VLAN settings.
- The native VLAN setting does not affect whether a VLAN is allowed or operational on a trunk.
- Allowing a VLAN on a trunk does not disable it; VLANs must be explicitly configured and active to forward traffic.
- Troubleshooting VLAN issues requires verifying VLAN presence, status, and trunk configuration on all involved switches.
- Exam candidates often mistake allowed VLAN lists as a complete solution, ignoring local VLAN operational state.
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.
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.
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.
CCNA DHCP practice questions
Practise DHCP scopes, relay, leases and troubleshooting.
CCNA show ip route practice questions
Practise routing-table output, longest-prefix match, AD and route selection.
CCNA show interfaces trunk practice questions
Practise trunk verification and VLAN forwarding across switches.
CCNA wireless security practice questions
Practise WLAN security, authentication and wireless architecture concepts.
CCNA IPv6 practice questions
Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.
More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
A VLAN must be locally defined and active on a switch for traffic to pass, even if it is allowed on the trunk link.
What is the correct answer to this question?
The correct answer is: Because the VLAN may still be absent, inactive, or otherwise not operational locally even if it is allowed on the trunk — A VLAN can still fail across a trunk even when it is allowed because the allowed list is only one part of the overall design. In plain language, a switch may permit the VLAN on the link, but if the VLAN does not actually exist locally, is not active, or if some other trunk characteristic is inconsistent, traffic can still fail. This is an important CCNA troubleshooting principle: one correct line of configuration does not guarantee the full end-to-end condition is correct. Candidates often stop at the allowed VLAN list because it is visible in common show commands. However, VLAN presence, local status, and other trunk parameters still matter. The best answer is the one recognizing that permission on the trunk does not automatically prove the entire VLAN path is healthy.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
Discussion
Loading comments…
Sign in to join the discussion.