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Difficulty: MediumTroubleshooting VLAN, Trunking, and Switching Issues

A network administrator is diagnosing two distinct layer 2 issues on Switch-A. First, syslog logs display repeated `%CDP-4-NATIVE_VLAN_MISMATCH` messages for trunk link interface GigabitEthernet0/1 connected to Switch-B. Second, interface statistics for GigabitEthernet0/2 connected to a local database server show a high number of late collisions and alignment errors during heavy transfer periods. Which of the following actions should the administrator take to resolve these issues? (Select TWO.)

  1. Reconfigure the native VLAN configuration on Switch-B's trunk interface to match the native VLAN setting on Switch-A.Answer
  2. Manually set matching speed and duplex settings on both Switch-A's GigabitEthernet0/2 interface and the database server's network interface card.Answer
  3. C
    Set the Spanning Tree Protocol (STP) priority on Switch-A to 65535 to force it to become the root bridge for all VLANs.
  4. D
    Replace the patch cable connecting Switch-A to the database server with a high-grade fiber optic jumper to eliminate late collisions.

Answer

The administrator should align the native VLAN configurations on both trunk ends (matching Switch-B to Switch-A) and ensure speed/duplex settings match on both Switch-A and the connected database server.
Correct troubleshooting requires addressing both specific symptoms reported: matching the native VLAN setting across the trunk link stops CDP mismatch alerts and frame misdirection, while hardcoding or autonegotiating matching duplex settings on both sides of the host interface eliminates late collisions.

Step-by-Step Solution

1
Analyze the CDP log message `%CDP-4-NATIVE_VLAN_MISMATCH`.
Identified an 802.1Q trunk misconfiguration where untagged frames are interpreted as belonging to different VLANs on opposite ends of the link.
802.1Q trunks must share identical native VLAN numbers on both interconnected switchports to prevent traffic misrouting and switchport error states.
2
Analyze interface statistics showing late collisions on GigabitEthernet0/2.
Identified a duplex mismatch between Switch-A (operating at half-duplex) and the connected server (operating at full-duplex).
Late collisions happen when a node detects a collision after transmitting the first 64 bytes of a frame, which occurs when one side ignores CSMA/CD rules due to full-duplex configuration while the other side uses half-duplex.
3
Select the appropriate remedial actions.
Reconfigure the trunk native VLAN on Switch-B and configure identical speed/duplex settings on GigabitEthernet0/2 and the server interface.
These steps address the root causes of trunk mismatches and duplex mismatches directly.

Key Concept

Troubleshooting 802.1Q Native VLAN Mismatches and Ethernet Duplex Mismatches
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Topics

Troubleshooting VLAN, Trunking, and Switching Issues

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