Problem Description

A university core switch is a stack of two S7712s with self-contained AC functionality, with downstream connections to OLT and AD9431, and separate down-hanging APs.

AD9431 and R250D alone are on-line normally, but AP4050DN under OLT cannot be on-line.

After the AD9431 is disconnected, the AP under OLT goes online successfully, and the fault must appear.

Alarm information

#Apr 16 2019 18:44:21 HX-S7712 L2IFPPI/4/MAC_FLAPPING_ALARM:OID 1.3.6.1.4.1.2011.5.25.42.2.1.7.12 The MAC address has flap value. (L2IfPort=0, entPhysicalIndex=0, BaseTrapSeverity=4, BaseTrapProbableCause=549, BaseTrapEventType=1, MacAddr=6008-1002-0fa0, VLANID=400, FormerIfDescName=Eth-Trunk1, CurrentIfDescName=Eth-Trunk9, DeviceName=HX-S7712)

#Apr 16 2019 18:39:01 HX-S7712 L2IFPPI/4/MAC_FLAPPING_ALARM:OID 1.3.6.1.4.1.2011.5.25.42.2.1.7.12 The MAC address has flap value. (L2IfPort=0, entPhysicalIndex=0, BaseTrapSeverity=4, BaseTrapProbableCause=549, BaseTrapEventType=1, MacAddr=6008-1002-0fa0, VLANID=400, FormerIfDescName=Eth-Trunk9, CurrentIfDescName=Eth-Trunk1, DeviceName=HX-S7712)

Processing

After adding the AD9431 upstream two interfaces to Eth-trunk through S7712 downstream configuration, the fault is solved.

Root Cause

Because the AD9431 downstream of S7712 is connected through a dual-link, Eth-trunk aggregation is configured on the S7712 side, but no aggregation is configured on the AD9431 side, resulting in a loop, which leads to MAC drift and failure of online connection of the AP under OLT.

Suggestions and summaries

1. Observe the failure phenomenon when the failure occurs, such as the emergence of MAC drift, the primary investigation of the loop problem.

2, the cause of the failure is not necessarily at this end, the need for global consideration.

3, Eth-trunk need to be configured at both ends at the same time, such as only in one side of the configuration alone in some cases can work properly, but will lead to problems such as loops, affecting the work of other equipment.