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Slow network rate caused by loop

Publication Date:  2017-08-13 Views:  347 Downloads:  0
Issue Description

The switch is connected to enterprise leased line users through a leased line. The switch functions as a Layer 2 aggregation switch, and the NE80 functions as the gateway.

The enterprise user reports that the slow service response problem.

Alarm Information



Handling Process

1- We checked the alarms by running command display trapbuffer and we found the alarm shown as below.

#Feb 23 2017 22:29:33-08:00 Huawei L2IFPPI/4/MFLPVLANALARM:OID 1.3.6.1.4.1.2011.5.25.160.3.7 MAC move detected, VlanId = 100, MacAddress = 0025-9e03-02f1, Original-Port = GE12/0/0, Flapping port = GE10/0/6 and GE12/0/0. Please check the network accessed to flapping port.

 2- We found that the MAC address 0025-9e03-02f1 is belong to the gateway in NE80. So we doubted that a loop existed on the downstream network attached to GE10/0/6. As a result, the MAC address of the NE80 flaps between GE10/0/6 and GE12/0/0 on the switch. When GE10/0/6 learns the MAC address of the NE80, traffic packets from users cannot be forwarded to the gateway.

3- Configure the MAC address of the gateway in NE80 as a static MAC address on GE12/0/0, then the slow network rate was resolved. 
[Huawei]mac-address static 5489-981e-0cb6 GigabitEthernet 12/0/0 vlan 100




 

Root Cause

A  loop existed on the downstream network attached to GE10/0/6. As a result, the MAC address of the NE80 flaps between GE10/0/6 and GE12/0/0 on the switch. When GE10/0/6 learns the MAC address of the NE80, traffic packets from users cannot be forwarded to the gateway.



Solution

1- Configure a static MAC address to prevents the loop Temporarily.

2- To eliminate the loop, configure a loop prevention protocol like STP/MSTP and so on.

Suggestions

To locate Layer 2 packet loss and intermittent disconnection problems, first check whether MAC address flapping occurs in addition to checking basic factors such as network cables, optical power of optical modules, and interface status. Then configure a static MAC address and check whether the problems are resolved. Configuring a static MAC address only prevents loops. To eliminate loops, configure a loop prevention protocol.



END