Case Study: An AP Fails to Go Online Again After Going Offline Unexpectedly, and the AP Status Is Displayed as cfgfa

Symptom

After an AP goes offline unexpectedly and attempts to go online again, the AP status is displayed as cfgfa (config-failed), indicating that the AP fails to go online.

Relevant Alarms and Logs

None

Cause Analysis

On a wired network, a third-party device abnormally sends a large number of multicast packets with unicast destination MAC addresses. As a result, the switch processes these multicast packets as unknown unicast packets and counts them as unicast packets.

Procedure

1. Check the AP online status.

   Run the display ap online-fail-record all command to check the reasons for AP's failures to go online.

   Run the display ap all command to check the AP status.

   The command output shows that the AP switches between the fault state and cfgfa state.

2. Ping the IP address of an AP on the AC to check the network connectivity between them.

   [AC] ping –c 20 x.x.x.x

   The ping result shows that severe packet loss occurs.

3. Run the following commands on the access switch to check whether a loop or abnormal broadcast/multicast packets exist on the wired network:
   1. Run the display mac-address flapping record command. No MAC address flapping record exists.
   2. Run the display stp brief command. STP is disabled.
   3. Run the display interface brief command. The traffic proportion of packets from the AC is the same as that of packets sent to the AP.
   4. Run the display interface gi0/0/X command. The number of outgoing unicast packets on the switch port directly connected to the AP increases greatly.

   In conclusion, the AP fails to go online due to severe packet loss caused by abnormal sent packet on the wired network.

4. Configure packet obtaining through bidirectional mirroring on the access switch port connected to the AP to determine the source of abnormal packets.

5. Disable the device from the network.

Suggestion and Summary

The methods of configuring mirroring on the devices are as follows:

Configure local mirroring on the AC:

<AC> system-view
[AC] observe-port interface gigabitethernet 0/0/2    //Configure GE0/0/2 as the local observing port.
[AC] interface gigabitethernet 0/0/1
[AC-GigabitEthernet0/0/1] mirror to observe-port both  //Mirror incoming and outgoing traffic on GE0/0/1 to GE0/0/2.

Configure local mirroring on the switch:

<Switch> system-view
[Switch] observe-port1 interface gigabitethernet 0/0/2      //Configure GE0/0/2 as the local observing port.
[Switch] interface gigabitethernet 0/0/1
[Switch-GigabitEthernet0/0/1] port-mirroring to observe-port 1 both //Mirror incoming and outgoing traffic on GE0/0/1 to GE0/0/2.