MAC Address Flapping Occurs Between Eth-Trunk Member Interfaces on the CE6850 Switches

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Issue Description

According to the customer, when the CE6850 switches form a stack with 10GE1/0/42 and 10GE2/0/42 being added to an Eth-Trunk and the stack is connected to a dual-NIC server, the stack repeatedly reports the alarm of the server's MAC address flapping on the two Eth-Trunk member interfaces.


Alarm Information

Dec 13 2017 16:33:00 68S02 %FEI_COMM/4/hwMflpVlanLoopAlarm_active(l):CID=0x807f042c-alarmID=0x095e0012;MAC flapping detected, VlanId = 8, Original-Port = 10GE1/0/42, Flapping port 1 = 10GE2/0/42, port 2 = -. Check the network connected to the interface learning a flapping MAC address : 02a0-98cc-9371.

Dec 13 2017 16:33:00 68S02 %FEI_COMM/4/hwMflpVlanLoopAlarm_clear(l):CID=0x807f042c-alarmID=0x095e0012-clearType=service_resume;Mac flapping detection recovered in vlan 8.

Dec 13 2017 16:17:01 68S02 %FEI_COMM/4/hwMflpVlanLoopAlarm_active(l):CID=0x807f042c-alarmID=0x095e0012;MAC flapping detected, VlanId = 8, Original-Port = 10GE1/0/42, Flapping port 1 = 10GE2/0/42, port 2 = -. Check the network connected to the interface learning a flapping MAC address : 02a0-98cc-9371.

Dec 13 2017 16:17:01 68S02 %FEI_COMM/4/hwMflpVlanLoopAlarm_clear(l):CID=0x807f042c-alarmID=0x095e0012-clearType=service_resume;Mac flapping detection recovered in vlan 8.


Handling Process

1. Check the Eth-Trunk status. It is found that the Eth-Trunk runs properly. No other exception log is generated and service forwarding on the Eth-Trunk is normal. It is suspected that the device reports alarm logs by mistake.

2. Run the reset mac-address flapping record command, which does not affect services. Check the alarm again. It is found that the MAC address flapping log is still displayed, but the alarm content is changed.

3. It is found that the MAC address flapping occurs between 10GE2/0/2 and Eth-Trunk12. After network loops are eliminated, the problem is resolved.


Root Cause

Multiple network loops occur on the network. In a fixed period of time, after the first network loop is eliminated, other MAC address flapping records can be displayed only after MAC address flapping records are cleared. Eliminate other network loops based on the newly displayed records.

According to the CE6850 product documentation, the MAC address flapping detection function can detect only the first loop in a VLAN within the aging period (5 minutes by default, which is configurable). For example, MAC address flapping occurs between PortA and PortB in a VLAN. After PortA or Port B goes Down and MAC address flapping occurs between PortC and PortD within the same aging period, the flapped interfaces in the alarm are still PortA and PortB.


Solution

         Clear the current MAC address flapping record and find the second loop on the device. After the loop is eliminated, the problem is resolved.


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