What to do when a MAC address flapping alarm is reported

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If the alarm is reported only once, ignore it.
If the alarm is reported multiple times, find the first and second interfaces where the MAC address is learned. Shut down the second interface to locate the loop. Then adjust the networking to remove the loop.

Other related questions:
When does a CE switch report an alarm after detecting MAC address flapping
In versions earlier than V100R005C10: A CE switch reports an alarm after detecting MAC address flapping for three times. The number of times cannot be configured. In V100R005C10 and later: By default, a CE switch reports an alarm after detecting MAC address flapping for 10 times. The number of times can be configured using the mac-address flapping detection [ security-level { low | middle | high } ] command.

How to clear MAC address flapping alarms on an AC
The possible causes for MAC address flapping alarms are as follows: - The interfaces where a loop occurs are added to the same VLAN. - Cables are connected incorrectly. - A loop occurs on the network. Troubleshooting procedure: 1. Connect cables on the interfaces correctly and check whether the alarm persists. If so, go to step 2. If not, go to step 6. 2. Check whether the two interfaces that learn the same MAC address can be added to different VLANs based on the network topology. If yes, go to step 3. If not, go to step 4. 3. Add the two interfaces to different VLANs, and check whether the alarm persists. If so, go to step 4. If not, go to step 6. 4. Disable loop detection and enable STP. Check whether the alarm persists. If so, go to step 5. If not, go to step 6. 5. Contact Huawei technical personnel. 6. End.

Meaning of MAC address flapping on S series switches
For S series switches (except the S1700), MAC address flapping occurs when a MAC address is learned by two interfaces in the same VLAN and the MAC address entry learned later overrides the earlier one. For example, in the MAC address entry with the MAC address 0011-0022-0034 and VLAN 2, the outbound interface is changed from Port1 to Port2. In this case, MAC address flapping occurs. MAC address flapping can cause an increase in the CPU usage on the switch. Generally, MAC address flapping occurs when a loop exists on the network. S series switches support MAC address flapping detection and take configured actions after detecting MAC address flapping.

How to solve MAC address flapping on S series switch
Firstly, check whether a loop occurs on the network. Secondly, use one of the following methods to prevent MAC address flapping: 1. Run the mac-address static mac-address command in the system view to configure static MAC addresses on an interface. 2. Configure the MAC address learning priority on an interface. That is, run the mac-learning priority priority-id command in the interface view on modular switches or S5720HI, S6720EI, and S5720EI fixed switches or run the mac-spoofing-defend enable command in the interface view on S5700LI, S5700S-LI, S5710-X-LI, S2750EI, S5720S-SI, and S5720SI fixed switches. After different MAC address learning priorities are configured for interfaces, only the MAC address entry learned by a high-priority interface can overwrite that learned by a low-priority interface if different interfaces have learned the same MAC address entry. This prevents MAC address flapping. Note that SA cards of modular switches do not support the MAC address learning priority configuration. You can run the undo mac-learning priority priority-id allow-flapping command in the system view to prohibit MAC address flapping between interfaces with the same priority.

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