CCNA Switching and Network Access Practice Question
Network Topology
A network engineer configures an EtherChannel between two Cisco switches SW1 and SW2 using LACP. After configuration, hosts connected to SW1 report intermittent connectivity to hosts on SW2. The engineer checks the EtherChannel status and sees that the trunk is up but only allows VLAN 1, while the hosts communicate across VLANs 10 and 20. Which command should the engineer apply to both switches to resolve the issue?
⚠ Common exam trap
Test-takers frequently assume the EtherChannel is fully functional once it shows as up/up, overlooking that the trunk's VLAN allowed list must match on both sides to pass traffic for all required VLANs.
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
✓
switchport trunk allowed vlan 1,10,20
The output shows the EtherChannel is up but only VLAN 1 is allowed on the trunk, while the hosts on SW1 and SW2 communicate across VLANs 10 and 20. Applying 'switchport trunk allowed vlan 1,10,20' on both switches ensures all necessary VLANs are permitted over the EtherChannel, resolving the intermittent connectivity caused by dropped traffic for VLANs 10 and 20.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
channel-group 1 mode active
Why it's wrong here
Reissuing `channel-group 1 mode active` is redundant because the interface configuration already places all member ports into port-channel 1 with LACP active negotiation, as evidenced by the operational state and LACP protocol. This command only defines the bundling method and negotiation mode; it does not affect which VLANs are permitted on the trunks. The intermittent connectivity stems from mismatched allowed VLAN lists across the physical port-channel members, not from the channel-group mode being inactive or incorrect.
- ✓
switchport trunk allowed vlan 1,10,20
Why this is correct
This command ensures that all member ports of the EtherChannel have the same VLAN list. Inconsistent allowed VLANs across member ports can cause traffic to be dropped intermittently. Applying this to all member interfaces on both switches resolves the issue.
- ✗
lacp rate fast
Why it's wrong here
The `lacp rate fast` command only changes the frequency of LACP control PDUs from 30 seconds to 1 second for faster link failure detection. It does not modify the VLAN allowed list, trunk mode, or any forwarding parameter that would cause intermittent traffic loss. Since this EtherChannel is already established under active LACP, altering the keepalive interval cannot resolve a member-port VLAN consistency issue.
- ✗
switchport mode trunk
Why it's wrong here
While `switchport mode trunk` is necessary for carrying multiple VLANs, it does not dictate the specific set of VLANs permitted on the interface. The interfaces are already operational trunk ports on the Layer 2 port-channel, so reapplying the mode command changes no actual parameter. The critical missing element is the allowed VLAN list—the `switchport trunk allowed vlan` command must be identical on every member to prevent the switch from dropping frames when hashing picks a port that does not have the destination VLAN.
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.
✓switchport trunk allowed vlan 1,10,20Correct answer▾
Why this is correct
This command ensures that all member ports of the EtherChannel have the same VLAN list. Inconsistent allowed VLANs across member ports can cause traffic to be dropped intermittently. Applying this to all member interfaces on both switches resolves the issue.
✗channel-group 1 mode activeWrong answer — click to see why▾
Why this is wrong here
The ports are already configured with LACP active mode, as indicated by the protocol being LACP and the ports being bundled. Reapplying this command does not address the root cause of intermittent connectivity, which is likely due to VLAN mismatch.
Why candidates choose this
Students might think that changing the LACP mode could fix the issue, but the mode is already correct. They may confuse mode active with other modes like passive or desirable.
✗lacp rate fastWrong answer — click to see why▾
Why this is wrong here
The 'lacp rate fast' command changes the LACP packet transmission rate to every second, which is used for faster failure detection. It does not affect VLAN consistency or cause intermittent connectivity; the issue is likely due to VLAN mismatch, not LACP rate.
Why candidates choose this
Students might associate 'fast' with improving performance or resolving connectivity issues, but this command is unrelated to VLAN configuration and would not fix the problem.
✗switchport mode trunkWrong answer — click to see why▾
Why this is wrong here
The ports are already configured as trunk ports (the Po1 is Layer2 and trunking is implied). Reapplying 'switchport mode trunk' does not address the VLAN inconsistency that causes intermittent connectivity.
Why candidates choose this
Students might think that ensuring trunk mode is set correctly could resolve the issue, but the problem is not about trunking mode; it's about inconsistent allowed VLANs across member ports.
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?”
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Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
LACP
LACP is a protocol that automatically combines multiple physical network links into a single logical link to increase bandwidth and provide redundancy.
Key term
EtherChannel
EtherChannel is a technology that bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.