How does MAC address flapping occur on improperly configured trunks?

Ask any question about Networking here... and get an instant response.

Post this Question & Answer:

How does MAC address flapping occur on improperly configured trunks?

Asked on Nov 26, 2025

Answer

MAC address flapping occurs on improperly configured trunks when the same MAC address is seen on different interfaces or VLANs, causing switches to rapidly update their MAC address tables. This typically happens due to misconfigurations in VLAN assignments or trunking protocols, leading to network instability and packet loss.

Example Concept: MAC address flapping on trunks often results from incorrect VLAN tagging or trunk misconfigurations, where a switch receives the same MAC address on multiple ports due to loops or incorrect trunk settings. This can cause the switch to continuously update its MAC address table, leading to network instability. Proper configuration of trunk ports, ensuring correct VLAN tagging, and using Spanning Tree Protocol (STP) can prevent such issues.

Additional Comment:

Ensure trunk ports are correctly configured with the appropriate VLANs.
Use Spanning Tree Protocol (STP) to prevent loops in the network.
Regularly monitor switch logs for MAC address flapping events.
Verify that VLAN configurations are consistent across all trunk links.

✅ Answered with Networking best practices.

Ask any question about Networking here... and get an instant response.