IPv6 uses Duplicate Address Detection (DAD) to detect conflicting IP addresses. PowerScale OneFS release 9.2 introduces support for Duplicate Address Detection (DAD). The DAD feature is disabled by default. To enable the DAD feature, use the isi_sysctl_cluster net.inet6.ip6.dad_count= command, where the dad_count value is the number of seconds. A value greater than zero for this command enables the DAD feature. It specifies the number of seconds OneFS checks for duplicate IP addresses when an IP address is initially configured. Setting the value to zero disables the DAD feature.
Note: The dynamic IP allocation method is not recommended with the DAD feature because it could lead to a DU event. The DU event occurs due to a potential race case in how dynamic IPs move between nodes leading to a false positive duplicated address. If this occurs, the IP will be unavailable until it moves again or is manually removed from the interface using ifconfig.
OneFS detects duplicate IP addresses on the front-end network through detection states. After an IP address is configured, OneFS sets the IP address to a tentative state. OneFS cannot listen on the IP address during the tentative state as it checks for a duplicate. If a duplicate is found, a duplicated flag is set on the IP address. If no duplicate IP addresses are found, the tentative flag is cleared, and OneFS starts listening on the IP address. The tentative and duplicated flags are displayed under the ifconfig command. Also, check the /var/log/messages kernel logs mentioning DAD complete.
The DAD feature also applies to SmartConnect SSIP addresses. If a duplicate SSIP address is detected, OneFS logs and removes the IP address. To confirm, check the /var/log/isi_smartconnect log file and search for duplicate address detection. Confirm SmartConnect has removed the SSIP by using the isi network interfaces list --type SSIP command.
Note: Dynamic IP and SSIP failover windows are increased by the number of seconds specified in the preceding sysctl command. OneFS allows the DAD process to complete before listening on an IP address.