Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
SW1# show interfaces trunk Port Mode Encapsulation Status Native vlan Gi0/1 on 802.1q trunking 1 Port Vlans allowed on trunk Gi0/1 10,20,30 SW2# show interfaces trunk Port Mode Encapsulation Status Native vlan Gi0/1 on 802.1q trunking 1 Port Vlans allowed on trunk Gi0/1 10,20,30,40
Based on the exhibit, which change would most likely restore connectivity for VLAN 40 across the inter-switch link?
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
Distractor review
Enable PPP on the trunk interfaces.
This is wrong because PPP is unrelated to Ethernet trunk forwarding.
B
Best answer
Add VLAN 40 to the allowed list on SW1 Gi0/1.
This is correct because VLAN 40 is missing from the allowed list on one side of the trunk.
C
Distractor review
Change the native VLAN to 40 on both switches.
This is wrong because the issue is the allowed VLAN list, not native VLAN mismatch.
D
Distractor review
Convert Gi0/1 into an access port on both switches.
This is wrong because the link is intended to carry multiple VLANs.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is to confuse native VLAN mismatches with allowed VLAN filtering issues. While native VLAN mismatches cause untagged frame problems, they do not selectively block VLAN traffic tagged with a specific VLAN ID. Another tempting mistake is to convert the trunk port into an access port, which disables multi-VLAN forwarding and breaks connectivity for all VLANs except one. Candidates may also incorrectly consider enabling PPP, which is irrelevant for Ethernet trunk links. The key is to focus on the allowed VLAN list because selective VLAN failures almost always point to VLAN filtering on the trunk.
Technical deep dive
How to think about this question
VLAN trunks are essential for carrying multiple VLANs across a single physical link between switches. A trunk port uses IEEE 802.1Q encapsulation to tag Ethernet frames with VLAN identifiers, allowing traffic from multiple VLANs to traverse the same link while maintaining VLAN separation. The trunk interface configuration includes specifying which VLANs are allowed to pass through the trunk, which is critical for ensuring connectivity for all intended VLANs. When a VLAN is missing from the allowed VLAN list on a trunk port, frames tagged with that VLAN ID are dropped and do not traverse the trunk. This selective filtering causes connectivity issues only for the affected VLAN, while other VLANs continue to function normally. The correct troubleshooting step is to verify and update the allowed VLAN list on both ends of the trunk to include all VLANs that need to communicate across the link. A common exam trap is confusing native VLAN mismatches or access port configurations with allowed VLAN filtering issues. While native VLAN mismatches can cause untagged frame problems, they do not selectively block tagged VLAN traffic. Similarly, converting a trunk to an access port removes multi-VLAN support entirely, which is not the intended solution here. Understanding the difference between trunk allowed VLAN lists and native VLAN settings is crucial for accurate diagnosis and resolution in Cisco switch environments.
KKey Concepts to Remember
- A trunk port uses 802.1Q tagging to carry traffic for multiple VLANs across a single physical link between switches.
- The allowed VLAN list on a trunk port determines which VLANs are permitted to send traffic across the trunk link.
- If a VLAN is missing from the allowed VLAN list on one side of a trunk, traffic for that VLAN is blocked and connectivity is lost.
- Native VLAN mismatches affect untagged traffic but do not block tagged VLAN traffic selectively on trunks.
- Converting a trunk port to an access port disables multi-VLAN traffic forwarding and is inappropriate for inter-switch links carrying multiple VLANs.
- PPP is a WAN protocol unrelated to Ethernet trunking and does not affect VLAN forwarding on switch trunk ports.
- Switches must have consistent allowed VLAN lists on both ends of a trunk to ensure VLAN traffic flows correctly.
- Selective VLAN connectivity issues often indicate allowed VLAN list mismatches rather than physical link or spanning-tree problems.
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.
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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 trunk port uses 802.1Q tagging to carry traffic for multiple VLANs across a single physical link between switches.
What is the correct answer to this question?
The correct answer is: Add VLAN 40 to the allowed list on SW1 Gi0/1. — The most likely fix is to allow VLAN 40 across the trunk on the switch where it is currently missing. In practical terms, the trunk is up and carrying some VLANs successfully, so the path is not completely broken. The selective failure for VLAN 40 points directly to the allowed VLAN list inconsistency shown in the output. This is still exam-realistic because it is a selective-switching failure, but it uses explicit operational output rather than a vague description.
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.
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