★ [WX3840H] A case study on frequent roaming and network disrupt caused by IPv6 address conflicts at a customer site

Customer feedback indicates that multiple Windows PCs with NICs enabling Internet Protocol Version 6, after connecting to our AP wireless network and obtaining IPv6 addresses assigned by the core, frequently roam among nearby APs with extremely poor network performance.

1. Use the command [AC]dis wlan mobility roam-track mac-address xxxx-xxxx-xxxx to confirm that the terminal MAC roams between multiple APs, with a frequency of several minutes.

2. After attempting to ping the IPv6 gateway, intermittent packet loss was observed, with normal connectivity for a few seconds followed by complete packet loss, occurring at a much higher frequency than roaming. This suggests the terminal may frequently go offline and back online.

3. Check the terminal online and offline history recorded in [AC-probe] dis system internal wlan client history-record mac-address xxxx-xxxx-xxxx. It can be seen that the terminal goes online and offline every second with reason code 5111, IP address conflict detected by AC. It is speculated that the IPv6 address of a certain device in the network conflicts with the customer device IPv6, causing the customer device to go offline.

4. Check that the collision detection (CSI) function of AC is enabled. Use the command dis wlan statistics client-ip-conflict to see the entry of the client PCs MAC address in the conflict list. It is concluded that the frequent roaming and network disrupt are caused by conflicting IPv6 addresses obtained by the terminal.

[workaround] [Sysname] undo wlan client ip-conflict enable Disable the collision detection (CSI) function of AC.

[Root cause analysis] On AC, use [AC-probe] dis system internal wlan client ip to check the IPv6 learning source and find that the conflicting IPv6 address is assigned by the core.

[IPv6 address collision detection (CSI) mechanism]
After enabling the IP address collision detection (CSI) function, you must also enable the IPv6 learning function for the IPv6 address collision detection (CSI) function to take effect. Once this function is active, the AP will intercept DHCPv6 or ND messages from terminals to learn their IPv6 addresses. If sta2s address is found to duplicate sta1s, the old terminal sta1 will be kicked off, and statistical information about the new and old clients with IP address conflicts will be generated. Additionally, the type of IPv6 conflicting address depends on whether the IPv6 learning method is configured as DN or DHCPv6.

wlan client ip-conflict-detection enable
display wlan statistics client-ip-conflict
client ipv6-snooping dhcpv6-learning enable
client ipv6-snooping nd-learning enable
client ipv6-snooping { dhcpv6-learning | nd-learning }