Case Study: APs Fail to Go Online Due to a CAPWAP Source IP Address Conflict

Symptom

In a VRRP HSB scenario, APs managed by an AC fail to go online after going offline.

Relevant Alarms and Logs

Related log:

ARP/4/ARP_LOG_DUPLICATE_IPADDR_DETECT: Detected an IP address collision.

Cause Analysis

The IP address of the VLANIF interface on the core switch conflicts with the VRRP virtual IP address (source IP address of the CAPWAP tunnel) of the AC.

Procedure

1. Check the AP status on the AC and network connectivity between the AC and AP.
   1. Run the display ap all command. The command output shows that a large number of APs are in cfg state.
   2. Run the display ap online-fail-record all command. The command output shows that a large number of APs fail to go online due to the reason of cfgfail.
   3. Run the display capwap configuration command to check that the CAPWAP source IP is on the same network segment as the AP's IP address.
   4. Run the ping –c 10 ap-ip command. The command output shows that the delay of the first ping operation is 200 ms and that of other ping operations is 1 ms.
   5. Run the ping –c 10 –s 1500 ap-ip command. The command output shows that the delay of the first ping packet is 200 ms and the delay of other ping packets is 1 ms.

2. Check whether MAC address flapping occurs on the core switch.

   Run the display mac-address flapping record command. The command output shows that MAC address flapping occurs on the AP management address segment.

   Run the display interface eth-trunk X command. The command output shows that a large number of broadcast and multicast packets exist on the interface.

   Run the reset counters interface command to clear interface records. Then run the preceding commands again. It is found that no MAC address flapping record or unexpected packets on the interface increases.

3. Check logs on the core switch to check for other exceptions.
   1. Run the display logbuffer command. The command output shows that a gateway IP address conflict occurs on the AP management address segment.
   2. Run the display arp ip-conflict track command to check that this IP address is always conflicting.
   3. Run the display ip interface brief command to check the interface where the conflicting IP address resides and the interface status.

4. Check the conflicting IP address on the AC.

   Run the display arp ip-conflict track and display vrrp commands in sequence to check that the conflicting IP address is the VRRP virtual IP address.

5. Check whether the VRRP status is normal.

   Run the display vrrp interface vlanif X command. The command output shows that the VRRP status of the master and backup ACs is normal.

6. According to the preceding troubleshooting process, the AP fails to go online because the interface address of the core switch conflicts with the AC's source address. Run the undo interface vlanif X command to delete the interface on the core switch. The problem is resolved.