Case Study: The Eth-Trunk Configuration Is Lost and a Loop Occurs on the Network, Causing APs to Go Offline Unexpectedly

Symptom

As shown in the following figure, the AC is deployed in off-path mode, and an Eth-Trunk is configured between the access switch and central AP. After the SD card of the central AP is replaced, the AP goes offline unexpectedly.

Relevant Alarms and Logs

None

Cause Analysis

After the SD card of the central AP is replaced, the Eth-Trunk configuration is lost.

Procedure

1. Packet loss occurs when the STA pings the core switch.
2. Run the display logbuffer command to check device logs. The command output shows that an OSPF router ID conflict occurs and the conflicting VLANs are all WLAN service VLANs. Therefore, a loop exists on the network. Then locate the port causing the loop.
3. Run the display mac-address flapping record command on the core switch. The command output shows that MAC address flapping has occurred.
4. Check the configuration and neighbor relationship of the abnormal interface on the core switch.
   1. Run the display interface brief command to check the port relationship and port traffic proportion.
   2. Run the display current-config interface eth-trunk Z command to check the Eth-Trunk configuration.
   3. Run the display lldp neighbor brief | interface gi y/y/y command to check the neighbor relationship and interconnection interfaces.

5. Repeat 3 and 4 on the downstream device to locate the loop point. It is found that the Eth-Trunk configuration of the interface connecting the central AP to the switch does not take effect.
6. Confirm with the customer whether the network or device is changed. The customer reports that the central AP is not restarted after the SD card is replaced.
7. Restart the central AP to make the Eth-Trunk configuration delivered from the AC to the central AP take effect.

Suggestion and Summary

The method for binding wired interfaces of the central AP to an Eth-Trunk is as follows:

[AC-wlan-view] wired-port-profile name wired-port1
[AC-wlan-wired-port-wired-port1] eth-trunk 0
[AC-wlan-view] wired-port-profile name wired-port2
[AC-wlan-wired-port-wired-port2] mode root
[AC-wlan-view] ap-group name ap-group1
[AC-wlan-ap-group-ap-group1] wired-port-profile wired-port1 xgigabitethernet 0
[AC-wlan-ap-group-ap-group1] wired-port-profile wired-port1 xgigabitethernet 1
[AC-wlan-ap-group-ap-group1] wired-port-profile wired-port2 eth-trunk 0

In addition, after the Eth-Trunk configuration is delivered, you need to restart the switch for the configuration to take effect.