Question

Difficulty: HardSwitching Concepts and VLANs

A network engineer is auditing Layer 2 switch operations to ensure proper frame encapsulation, VLAN trunking, CAM table management, and port access controls across campus switches. Match each switching concept on the left with its corresponding operational behavior on the right.

  • IEEE 802.1Q TaggingAppends a 4-byte field containing a Tag Protocol Identifier and VLAN ID between the Source MAC address and EtherType field of an Ethernet frame.
  • Native VLAN ProcessingAssigns incoming untagged frames on an 802.1Q trunk interface to a specific pre-configured internal broadcast domain without modifying frame headers.
  • MAC Address Table AgingClears dynamic Content Addressable Memory (CAM) entries after a defined period of port inactivity to ensure accurate frame forwarding following topology changes.
  • Sticky Port SecurityAutomatically saves dynamically learned MAC addresses on a switch interface into the active running configuration to survive port state resets.

Answer

IEEE 802.1Q Tagging matches insertion of a 4-byte header containing a TPID and VLAN ID; Native VLAN Processing matches assigning untagged trunk frames to a default internal broadcast domain without adding tags; MAC Address Table Aging matches clearing dynamic CAM entries following inactivity; Sticky Port Security matches converting dynamically learned MAC addresses into running configuration entries.
Each concept correctly maps to its foundational Layer 2 operational role: IEEE 802.1Q handles 4-byte header insertion, Native VLAN handles untagged trunk traffic mapping, MAC table aging handles CAM cache flushing upon inactivity, and sticky port security writes dynamic MAC addresses to the running configuration.

Step-by-Step Solution

1
Analyze frame encapsulation mechanisms for VLAN trunking.
Identify IEEE 802.1Q tagging as the process of inserting a 4-byte tag field into the Ethernet frame structure between the Source MAC address and the EtherType field.
This allows trunk links to multiplex traffic from multiple VLANs over a single physical connection.
2
Evaluate trunk handling of untagged traffic.
Identify Native VLAN processing as the mechanism that routes untagged frames received on an 802.1Q trunk into the configured native VLAN without adding explicit 802.1Q tags.
Backward compatibility and control traffic (such as CDP or STP) rely on untagged transmission across trunks.
3
Determine Layer 2 switch CAM table maintenance procedures.
Associate MAC Address Table Aging with the automatic removal of idle dynamic MAC entries from the CAM table after the aging timer expires.
This ensures the switch adapts dynamically when network hosts disconnect or move to different switch ports.
4
Examine port security persistence features.
Connect Sticky Port Security to the automatic conversion of dynamically learned source MAC addresses into running configuration statements.
Sticky learning avoids manual static MAC configuration while preserving host port restrictions across interface reboots.

Key Concept

Layer 2 Switching Mechanisms and VLAN Trunking Operations
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