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Difficulty: MediumSwitching Concepts and VLANs

A network administrator is designing a local network topology across two switches using multiple VLANs and an 802.1Q trunk link. Which TWO of the following statements correctly describe Layer 2 switch operations and VLAN encapsulation in this environment?

  1. VLANs partition a physical switch into multiple distinct Layer 2 broadcast domains.Answer
  2. The switch inserts a 4-byte 802.1Q tag into the Ethernet frame header when forwarding traffic for non-native VLANs across a trunk link.Answer
  3. C
    Workstations assigned to different VLANs on the same physical switch can communicate directly at Layer 2 without a Layer 3 routing device.
  4. D
    Untagged frames arriving at an 802.1Q trunk interface are discarded by default to prevent frame corruption.
  5. E
    Increasing the STP bridge priority to the maximum numerical value ensures a switch will be elected as the Spanning Tree Root Bridge.

Answer

VLANs partition a physical switch into distinct Layer 2 broadcast domains, and an 802.1Q trunk inserts a 4-byte tag header into Ethernet frames for non-native VLAN traffic.
VLANs create logically separate Layer 2 broadcast domains on a physical switch, restricting broadcast traffic and isolating subnets. Across trunk connections, IEEE 802.1Q multiplexes VLAN traffic by inserting a 4-byte tag header into standard Ethernet frames for non-native VLANs.

Step-by-Step Solution

1
Analyze the fundamental definition and purpose of VLAN segmentation at Layer 2.
Confirm that each VLAN functions as an isolated broadcast domain within the switch infrastructure.
Traffic broadcasted within one VLAN does not cross over to ports in another VLAN without Layer 3 routing.
2
Examine how 802.1Q trunking multiplexes traffic from multiple VLANs across a single physical link.
Identify that 802.1Q inserts a 4-byte VLAN tag into the frame header for non-native VLAN traffic.
Tagging allows receiving switches to correctly identify the destination VLAN of incoming frames.
3
Evaluate the incorrect statements regarding inter-VLAN routing, native VLAN frame handling, and STP priority.
Reject statements claiming direct Layer 2 inter-VLAN communication, untagged frame dropping on trunks, and high numerical STP priority root selection.
Inter-VLAN traffic requires Layer 3 routing, native VLAN handles untagged traffic, and STP prefers lower bridge priority values.

Key Concept

VLAN Broadcast Isolation and 802.1Q Trunk Tagging
Estimated Time:1m 30s
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Topics

Switching Concepts and VLANs

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