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Difficulty: MediumVLAN Configuration and 802.1Q Trunking

A network administrator is connecting a wireless access point (AP) to switch port GigabitEthernet 1/0/5. The AP transmits management traffic untagged on VLAN 100, while wireless user traffic on the 'Guest' SSID is transmitted with an 802.1Q tag for VLAN 200. The switch port is currently operating with default 802.1Q trunk settings, where VLAN 1 is the default native VLAN. Which interface configuration command must be executed on Switch GigabitEthernet 1/0/5 so that untagged management frames are correctly processed on VLAN 100?

  1. switchport trunk native vlan 100Answer
  2. B
    switchport trunk allowed vlan 100,200
  3. C
    switchport access vlan 100
  4. D
    switchport voice vlan 100

Answer

The command 'switchport trunk native vlan 100' correctly designates VLAN 100 as the native VLAN on the 802.1Q trunk interface.
On an IEEE 802.1Q trunk link, untagged frames are associated with the port's native VLAN. By default, Cisco switches assign VLAN 1 as the native VLAN. Issuing the command 'switchport trunk native vlan 100' changes this mapping so that all untagged traffic (in this case, AP management traffic) is placed into VLAN 100 while maintaining 802.1Q tagging for VLAN 200.

Step-by-Step Solution

1
Analyze the framing requirements for the connected network device
Management traffic requires untagged framing for VLAN 100, and Guest traffic requires tagged 802.1Q framing for VLAN 200.
802.1Q trunks pass tagged frames for specified VLANs and untagged frames for a single designated native VLAN.
2
Identify the switch port's current state and necessary modification
The trunk defaults to VLAN 1 as the native VLAN. Untagged traffic will inadvertently enter VLAN 1 unless reconfigured.
To route untagged management frames into VLAN 100, the switch port's native VLAN ID must be explicitly changed from VLAN 1 to VLAN 100.
3
Select the appropriate interface CLI command
Executing 'switchport trunk native vlan 100' maps untagged ingress and egress frames to VLAN 100.
This command specifically redefines the 802.1Q native VLAN for the trunk port without disrupting tagged VLAN 200 traffic.

Key Concept

802.1Q Native VLAN Configuration
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Topics

VLAN Configuration and 802.1Q Trunking

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