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Difficulty: MediumSwitching Concepts and VLANs

A network technician is configuring and auditing Layer 2 features on an enterprise switch stack. Match each Layer 2 switching concept on the left to its correct operational description on the right.

  • 802.1Q EncapsulationInserts a 4-byte field into the Ethernet frame header to identify VLAN traffic across trunk links.
  • Native VLANProcesses untagged frames received on an 802.1Q trunk interface.
  • Port SecurityRestricts switch port access based on source MAC address learning thresholds or explicit definitions.
  • Spanning Tree ProtocolPrevents Layer 2 loops by placing redundant switch ports into a non-forwarding state.

Answer

802.1Q Encapsulation matches with inserting a 4-byte VLAN field into the Ethernet header. Native VLAN matches with processing untagged frames on trunk ports. Port Security matches with restricting access based on source MAC addresses. Spanning Tree Protocol matches with placing redundant ports in a non-forwarding state to prevent loops.
Each Layer 2 switching feature directly matches its operational behavior: 802.1Q inserts a 4-byte header for trunk tagging; Native VLAN handles untagged frames on trunk links; Port Security restricts ingress based on source MAC address rules; and Spanning Tree Protocol blocks redundant ports to avoid Layer 2 loops.

Step-by-Step Solution

1
Identify the primary frame tagging mechanism used across Layer 2 trunk interfaces.
802.1Q Encapsulation modifies standard Ethernet frames by adding a 4-byte header tag containing the VLAN ID.
Trunk links require frame tagging to distinguish frames belonging to different logical networks.
2
Determine how unencapsulated (untagged) frames are processed on an 802.1Q trunk port.
The Native VLAN is assigned to process any untagged frames sent or received across an 802.1Q trunk link.
Backward compatibility and explicit handling of control traffic require a designated default untagged path.
3
Analyze Layer 2 access control mechanisms on individual switch interfaces.
Port Security enforces MAC address limits on switch ports to restrict unauthorized network devices.
Evaluating ingress source MAC addresses prevents unauthorized physical network additions.
4
Examine loop suppression protocols in redundant switch topologies.
Spanning Tree Protocol blocks specific redundant switch ports to maintain a loop-free logical forwarding topology.
Broadcast storms caused by physical redundant paths must be mitigated at Layer 2.

Key Concept

Core Layer 2 Switching Concepts and VLAN Operation Mechanics
Estimated Time:1m 30s
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Topics

Switching Concepts and VLANs

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