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Difficulty: MediumVLAN Configuration and 802.1Q Trunking

A network administrator is configuring interface `GigabitEthernet1/0/12` on a switch to connect to a multi-tenant device. The device sends tagged frames for VLAN 200 (Data) and untagged frames for device management. The administrator needs to ensure that untagged management frames are assigned to VLAN 50 while allowing tagged VLAN 200 frames across the link. Which configuration snippet correctly satisfies these requirements?

  1. switchport mode trunk
    switchport trunk native vlan 50
    switchport trunk allowed vlan 50,200    Answer
  2. B
    switchport mode trunk
    switchport access vlan 50
    switchport trunk allowed vlan 200
  3. C
    switchport mode access
    switchport access vlan 50
    switchport access vlan 200
  4. D
    switchport mode trunk
    switchport trunk native vlan 200
    switchport trunk allowed vlan 50

Answer

The correct configuration enables 802.1Q trunking on the switchport, sets native VLAN 50 to process untagged management frames, and includes both VLAN 50 and VLAN 200 in the allowed VLAN list.
The correct choice configures the interface in trunking mode, sets the native VLAN to 50 (which maps all untagged incoming frames to VLAN 50), and permits both VLAN 50 and VLAN 200 across the trunk link.

Step-by-Step Solution

1
Identify the trunking requirement
The link must carry both tagged traffic (VLAN 200) and untagged traffic (Management), requiring an 802.1Q trunk configuration.
Access mode interfaces support only one untagged VLAN, whereas trunks support multiple VLANs over a single physical port.
2
Map untagged traffic to the target management VLAN
Set the native VLAN on the trunk to 50 using `switchport trunk native vlan 50`.
By default, 802.1Q trunks assign untagged frames to VLAN 1; defining a custom native VLAN redirects untagged frames to VLAN 50.
3
Verify allowed VLAN list
Include VLAN 50 and VLAN 200 using `switchport trunk allowed vlan 50,200`.
Both the native VLAN and tagged VLANs must be permitted on the trunk interface to allow bidirectionally passed frames.

Key Concept

802.1Q Native VLAN & Trunk Allowed List Configuration
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Topics

VLAN Configuration and 802.1Q Trunking

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