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Difficulty: EasyVLAN Configuration and 802.1Q Trunking

A network technician is configuring an IEEE 802.1Q trunk link between two switches. By default, how does an 802.1Q trunk port process outgoing frames belonging to the native VLAN?

  1. It forwards the frames across the trunk link without inserting an 802.1Q header tag.Answer
  2. B
    It inserts a 4-byte 802.1Q header tag containing the native VLAN ID into every frame.
  3. C
    It drops all untagged native VLAN frames because 802.1Q trunk ports only permit tagged traffic.
  4. D
    It routes the untagged frames directly to other VLANs without requiring a Layer 3 device.

Answer

By default, an IEEE 802.1Q trunk port forwards outgoing frames belonging to the native VLAN across the trunk link without inserting an 802.1Q header tag.
Under the IEEE 802.1Q standard, frames belonging to the native VLAN (VLAN 1 by default) are transmitted across trunk links without adding an 802.1Q tag header. When the receiving switch receives an untagged frame on a trunk interface, it automatically assigns that frame to its configured native VLAN.

Step-by-Step Solution

1
Identify the standard tagging mechanism used by IEEE 802.1Q on trunk links.
IEEE 802.1Q inserts a 4-byte tag into Ethernet frames to identify VLAN membership for tagged VLANs.
Tagging allows multiple VLANs to share a single physical trunk link while maintaining logical separation.
2
Determine the special exception for native VLAN traffic on an 802.1Q trunk.
Frames associated with the native VLAN are forwarded across the trunk without receiving an 802.1Q tag header.
Backward compatibility with legacy non-trunking devices requires one VLAN's traffic to remain untagged.

Key Concept

IEEE 802.1Q Native VLAN Tagging Behavior
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Topics

VLAN Configuration and 802.1Q Trunking

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