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Difficulty: MediumSwitching Concepts and VLANs

A network host connected to Switch Port 1 (configured as a Layer 2 access port in VLAN 10) transmits a unicast Ethernet frame destined for a host on Switch Port 2 (also an access port in VLAN 10). The switch's MAC address table already contains an active, valid entry mapping the destination MAC address to Switch Port 2. Which of the following operations will the switch perform upon receiving the frame?

  1. Inspect the destination MAC address, identify the matching entry for Switch Port 2, and forward the untagged frame exclusively out Switch Port 2.Answer
  2. B
    Insert a 4-byte 802.1Q VLAN header containing VLAN ID 10 into the frame before transmitting it out Switch Port 2.
  3. C
    Flood the frame out all active interfaces across all VLANs on the switch except Switch Port 1 to locate the destination host.
  4. D
    Decapsulate the frame header, evaluate the Layer 3 IP header, and route the packet directly to the default gateway before forwarding it to Switch Port 2.

Answer

The switch inspects the destination MAC address, identifies the matching MAC address table entry for Switch Port 2, and forwards the untagged frame exclusively out Switch Port 2.
When a switch receives a unicast frame on an access port, it looks up the destination MAC address in its MAC address table. Since the address is present (known unicast) and belongs to the same VLAN, the switch forwards the frame directly out the associated port (Switch Port 2) without adding 802.1Q tags.

Step-by-Step Solution

1
Analyze the incoming frame and port mode configuration
The frame arrives on Switch Port 1, which is assigned as an access port in VLAN 10.
Access ports accept untagged frames and associate them internally with their configured VLAN.
2
Perform a MAC address table lookup for the destination address
A matching entry is found linking the destination MAC address directly to Switch Port 2.
Known unicast entries allow the switch to perform microsegmentation and forward traffic directly to the target port.
3
Determine the egress frame handling for an access port
The frame is egressed out Switch Port 2 in standard untagged Ethernet frame format.
802.1Q tags are stripped or never added on access ports connected to end hosts.

Key Concept

Switching Concepts and VLAN Forwarding Logic
Estimated Time:1m 15s
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Topics

Switching Concepts and VLANs

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