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Difficulty: MediumSwitching Concepts and VLANs

A network administrator configures a single Layer 2 switch with VLAN 10 (Sales) and VLAN 20 (Marketing). Access ports are assigned to their respective VLANs, but no Layer 3 routing device or inter-VLAN routing interface is present. When a host on VLAN 10 transmits an Ethernet broadcast frame, how does the switch handle the frame?

  1. A
    The switch floods the broadcast frame to all active ports assigned to VLAN 10 and VLAN 20 across the switch.
  2. The switch forwards the frame exclusively out of all active ports assigned to VLAN 10, except the port on which it arrived.Answer
  3. C
    The switch strips the Layer 2 header, converts the frame to a Layer 3 packet, and routes it to VLAN 20.
  4. D
    The switch encapsulates the broadcast frame with an 802.1Q tag and forwards it out untagged access ports on VLAN 20.

Answer

The switch forwards the broadcast frame exclusively out of all active ports assigned to VLAN 10, except the port on which it arrived.
Virtual Local Area Networks (VLANs) segment a single physical switch into multiple distinct Layer 2 broadcast domains. When an ingress access port receives a broadcast frame, the switch floods that frame exclusively out of other active access ports assigned to the exact same VLAN (excluding the receiving port). Devices in different VLANs cannot receive Layer 2 broadcast frames from each other without a Layer 3 inter-VLAN routing mechanism.

Step-by-Step Solution

1
Identify the type of traffic received
The incoming traffic is an Ethernet broadcast frame (destination MAC address `FF:FF:FF:FF:FF:FF`).
Broadcast frames must be flooded out of all interfaces within the originating broadcast domain.
2
Evaluate the VLAN boundary configuration
The receiving port belongs to VLAN 10. A VLAN defines a logical Layer 2 broadcast domain.
Traffic inside one broadcast domain is logically isolated from other broadcast domains (VLAN 20) at Layer 2.
3
Determine switch forwarding behavior
The switch replicates the broadcast frame only to active member ports of VLAN 10, omitting the ingress port and ports assigned to VLAN 20.
Without a Layer 3 router or inter-VLAN routing configured, frames cannot traverse between separate VLANs.

Key Concept

VLAN Broadcast Isolation
Estimated Time:1m 0s
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Topics

Switching Concepts and VLANs

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