350-601 Network Practice Question
Exhibit
Refer to the exhibit. ! Nexus 9000 switch interface Ethernet1/1 switchport mode trunk switchport trunk allowed vlan 10,20,30 spanning-tree port type edge trunk no shutdown ! Switchport statistics Ethernet1/1 is up, line protocol is up Hardware: 1000/10000 Ethernet, address: xxxx.xxxx.xxxx Description: Server connection MTU 1500 bytes Port mode is trunk Trunk encapsulation is 802.1Q Trunk allowed vlans: 10,20,30 Trunk native vlan: 1 Vlans allowed on trunk: 10,20,30 Vlans active and untagged: 1 Vlans active and tagged: 10,20,30 interface port-channel1 switchport mode trunk switchport trunk allowed vlan 10,20,30 spanning-tree port type edge trunk no shutdown
A server connected to Ethernet1/1 is unable to communicate on VLAN 1. The server is configured to send untagged frames. Based on the exhibit, what is the most likely cause?
⚠ Common exam trap
Cisco often tests the misconception that untagged frames are always allowed on a trunk port, but the trap here is that the native VLAN must be explicitly permitted in the allowed VLAN list; otherwise, untagged frames are dropped even if the port is up and configured as a trunk.
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
✓
VLAN 1 is not allowed on the trunk, so untagged frames are dropped.
The server sends untagged frames, which are placed into the native VLAN of the trunk port. By default, the native VLAN is VLAN 1. However, if VLAN 1 is explicitly removed from the allowed VLAN list on the trunk (e.g., with 'switchport trunk allowed vlan remove 1'), the switch will drop all frames belonging to that VLAN, including untagged frames that would otherwise be classified into VLAN 1. This matches the exhibit where the port is configured as a trunk but VLAN 1 is not allowed, causing the server's traffic to be dropped.
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 spanning-tree port type edge trunk is causing BPDU guard to block the port.
Why it's wrong here
Port type edge trunk enables PortFast but does not block traffic on untagged VLAN.
- ✗
The port is in err-disabled state due to a loop.
Why it's wrong here
The port is up and line protocol is up.
- ✓
VLAN 1 is not allowed on the trunk, so untagged frames are dropped.
Why this is correct
Untagged frames are placed in native VLAN 1, but VLAN 1 is not in the allowed list.
- ✗
The port is administratively down.
Why it's wrong here
The no shutdown command is present.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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