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Difficulty: MediumSwitching Concepts and VLANs

A network host connected to interface FastEthernet 0/120/12 on a Layer 2 switch transmits an Address Resolution Protocol (ARP) request broadcast frame. Interface FastEthernet 0/120/12 is configured as an access port belonging to VLAN 5050. Which of the following actions will the switch perform upon receiving this frame?

  1. The switch forwards the frame out all operational access ports assigned to VLAN 5050, excluding interface FastEthernet 0/120/12.Answer
  2. B
    The switch floods the frame out all operational ports across all configured VLANs on the switch, excluding interface FastEthernet 0/120/12.
  3. C
    The switch strips the Layer 2 Ethernet headers and converts the broadcast frame into a Layer 3 IP packet before forwarding.
  4. D
    The switch inserts an 802.1Q VLAN header tag into the frame before forwarding it out all other access ports assigned to VLAN 5050.

Answer

The switch forwards the broadcast frame out all active access ports configured for VLAN 50, excluding the receiving port FastEthernet 0/12.
A Virtual Local Area Network (VLAN) creates a logical Layer 2 broadcast domain. When a broadcast frame (such as an ARP request) is received on an access port, the switch floods that frame to every active port belonging to the same VLAN, while excluding the port on which the frame originally arrived to prevent loops.

Step-by-Step Solution

1
Identify the frame type and ingress port configuration.
The frame is an ARP request broadcast (destination MAC ff:ff:ff:ff:ff:ff) arriving on access port FastEthernet 0/12 assigned to VLAN 50.
Understanding the PDU type and port membership determines how the switch handles forwarding.
2
Determine the Layer 2 broadcast domain boundary.
VLAN 50 forms a logical Layer 2 broadcast domain isolated from all other VLANs on the switch.
Broadcast frames are contained strictly within the originating VLAN.
3
Apply Layer 2 switch flooding behavior rules.
The switch floods the broadcast frame to all active interfaces assigned to VLAN 50, except the ingress port FastEthernet 0/12, without applying 802.1Q tags to access port output.
Standard switch logic dictates flooding broadcast traffic within the VLAN while preventing loopback to the source port.

Key Concept

VLAN Broadcast Domain Boundaries and Layer 2 Flooding Logic
Estimated Time:1m 15s
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Topics

Switching Concepts and VLANs

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