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Difficulty: MediumSwitching Concepts and VLANs

A network administrator connects two workstations, Host A and Host B, to access ports on the same physical Layer 2 switch. Host A is configured on VLAN 10 (192.168.10.0/24), while Host B is configured on VLAN 20 (192.168.20.0/24). Host A transmits an ARP broadcast frame to determine an IP address on its local network segment. How will the switch handle this broadcast frame?

  1. The switch floods the broadcast frame out all ports assigned to VLAN 10 except the receiving port, preventing Host B on VLAN 20 from receiving it.Answer
  2. B
    The switch forwards the broadcast frame to all active ports across both VLANs because all interfaces reside on the same physical switch hardware.
  3. C
    The switch inspects the target Layer 3 IP address inside the ARP request and routes the packet directly to Host B on VLAN 20.
  4. D
    The switch strips the VLAN 10 identifier from the frame header and redirects it to VLAN 20 as untagged native VLAN traffic.

Answer

The switch floods the broadcast frame out all ports assigned to VLAN 10 except the receiving port, preventing Host B on VLAN 20 from receiving it.
A Virtual Local Area Network (VLAN) creates a logical boundary at Layer 2. Broadcast frames transmitted by a device are flooded only to interfaces within the exact same VLAN membership (excluding the receiving interface). Consequently, Host B on VLAN 20 is shielded from VLAN 10 broadcast traffic.

Step-by-Step Solution

1
Identify the frame type and ingress interface configuration.
The incoming frame is an Ethernet broadcast frame (destination MAC FF:FF:FF:FF:FF:FF) originating from a host assigned to VLAN 10.
VLAN memberships assigned to switch interfaces define the boundary for Layer 2 broadcast containment.
2
Determine Layer 2 switch forwarding behavior for broadcast traffic within a VLAN.
The switch replicates the broadcast frame to all operational interfaces that belong to VLAN 10, excluding the port where the frame entered.
VLANs act as independent logical switches; frames in one VLAN are isolated from interfaces assigned to other VLANs.
3
Evaluate the impact on hosts in different VLANs.
Host B, residing on an access port configured for VLAN 20, does not receive the broadcast frame.
Without a Layer 3 routing mechanism (such as a router or Layer 3 switch), traffic cannot cross VLAN boundaries.

Key Concept

VLAN Broadcast Domain Isolation
Estimated Time:1m 15s
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Topics

Switching Concepts and VLANs

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