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Difficulty: EasyInterswitch Connectivity and Trunking (802.1Q)

A switch interface configured as an IEEE 802.1Q trunk receives an Ethernet frame that does not contain a 4-byte 802.1Q VLAN tag. How does the switch process this incoming frame?

  1. It assigns the frame to the native VLAN configured on the trunk port.Answer
  2. B
    It drops the frame because 802.1Q trunks require all incoming frames to be tagged.
  3. C
    It automatically forwards the frame on all active access ports regardless of VLAN assignment.
  4. D
    It immediately places the trunk port into a blocking state to prevent a Layer 2 loop.

Answer

The switch assigns the untagged frame to the native VLAN configured on the trunk port.
Under IEEE 802.1Q trunking standards, traffic belonging to the configured native VLAN is transmitted across the trunk link without inserting a 4-byte VLAN tag. When an untagged frame arrives at an 802.1Q trunk interface, the receiving switch assigns that frame to its configured native VLAN.

Step-by-Step Solution

1
Examine frame encapsulation on the 802.1Q trunk link.
Identify that the incoming frame lacks a 4-byte 802.1Q VLAN tag header.
802.1Q trunking transmits and receives native VLAN traffic without appending a VLAN tag.
2
Apply 802.1Q native VLAN processing rules.
Map the untagged frame to the native VLAN assigned to the trunk interface.
Standard 802.1Q mechanics dictate that untagged frames arriving on a trunk interface belong to the configured native VLAN.

Key Concept

802.1Q Native VLAN untagged frame handling
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Topics

Interswitch Connectivity and Trunking (802.1Q)

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