Revelations of troubleshooting for CE switches �?Alarm for MAC address flapping

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To troubleshoot this fault, you can refer to the revelations of troubleshooting for CE switches. For details, see the page on the right.

Other related questions:
In which situation does MAC address flapping occur on CE switches
MAC address flapping occurs when a MAC address is learned by two interfaces in the same VLAN and the MAC address entry learned later replaces the earlier one. MAC address flapping is usually caused by Layer 2 loops.

After an interface on a CE switch becomes Up during the aging time, will the switch still detect MAC address flapping during the remaining aging time
The default aging time of flapped MAC addresses is 300 seconds. You can run the error-down auto-recovery cause mac-address-flapping interval interval-value command to configure it. After the command is executed, if MAC address flapping stops and the interface becomes Up after the delay, the CE switch no longer detects MAC address flapping during the remaining aging time. This is because the aging time does not expire. If detection on MAC address flapping is required, it is recommended that the delay for an interface to automatically become Up be set greater than the aging time of flapped MAC addresses.

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.

Revelations of troubleshooting-SSH login failure
If logging to the SSH server through STelnet fails, check the following configuration: 1. Check whether the SSH service is enabled on the SSH server. 2. Check whether the access protocol is correctly configured in the VTY user interface view. 3. Check whether an RSA public key is configured on the SSH server. 4. Check whether an SSH user is configured on the SSH server. 5. Check whether the number of login users on the SSH server reaches the upper limit. 6. Check whether an ACL is bound to the VTY user interface of the SSH server. 7. Check the SSH version on the SSH client and server. 8. Check whether first-time authentication is enabled on the SSH client.

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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