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Difficulty: HardSwitching Concepts and VLANs

Match each Layer 2 switching mechanism on the left with its corresponding operational behavior or frame processing rule on the right.

  • 802.1Q Native VLAN TrunkingMaps incoming untagged frames to the configured default VLAN and transmits egress frames for that VLAN across the trunk link without an 802.1Q header tag.
  • Unknown Unicast FloodingReplicates ingress frames targeting unrecorded MAC addresses to all active ports belonging to the same VLAN, excluding the ingress port.
  • STP Topology Change Notification (TCN)Temporarily reduces the MAC address table aging timer to the forward delay duration to flush stale Layer 2 forwarding entries.
  • Port Security Restrict ModeDrops ingress traffic from unauthorized MAC addresses, increments the security violation counter, and generates an SNMP/Syslog alert while keeping the interface operationally active.

Answer

The concepts match their operational behaviors as follows: 802.1Q Native VLAN Trunking maps untagged traffic to the native VLAN and transmits it without 802.1Q headers; Unknown Unicast Flooding replicates frames with unknown destination MACs out all ports within the same VLAN except the receiving port; STP Topology Change Notification (TCN) reduces the CAM aging timer to the forward delay setting to purge invalid paths; Port Security Restrict Mode drops unauthorized frames and logs violations while keeping the interface active.
Each Layer 2 operational concept is matched to its exact specification: 802.1Q Native VLAN handles untagged trunk traffic without headers; Unknown Unicast Flooding distributes unmapped destination unicast frames within the VLAN domain; STP TCN reduces the MAC address table aging duration to force fast re-learning; Port Security Restrict Mode drops non-permitted MAC traffic and generates violation logs while keeping the port up.

Step-by-Step Solution

1
Analyze 802.1Q trunking behavior regarding untagged frame processing.
Identify that the Native VLAN feature handles untagged ingress frames and strips 802.1Q headers on egress for that specific VLAN.
The 802.1Q standard relies on native VLAN designations for backward compatibility with non-tagging switch ports and control traffic.
2
Examine switch forwarding logic when a destination MAC address is absent from the CAM table.
Associate unknown unicast traffic with flooding across all active ports within the frame's ingress VLAN except the receiving port.
Switches must deliver unicast frames even when host port locations have not yet been learned, while maintaining strict VLAN isolation.
3
Evaluate CAM table management during Spanning Tree Protocol (STP) topology convergence.
Match STP TCN frame processing with shortening the CAM aging timer from 300 seconds down to the forward delay parameter (e.g., 15 seconds).
Reducing the aging timer rapidly purges outdated MAC mappings caused by link changes without forcing an immediate full table clear.
4
Differentiate between switch port security violation modes (Protect, Restrict, and Shutdown).
Connect Restrict mode to dropping non-permitted traffic, logging Syslog/SNMP notifications, and keeping the port online.
Restrict mode actively logs security events while maintaining interface availability, distinguishing it from Protect (silent drop) and Shutdown (err-disable interface).

Key Concept

Layer 2 Switch Forwarding Logic, VLAN Control Operations, and Port Security Behavior
Estimated Time:2m 30s
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Topics

Switching Concepts and VLANs

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