DAD Overview

When enabled on a user VR or VR-Default, the Duplicate Address Detection (DAD) feature runs when an IP interface is initialized or when a CLI command initiates a DAD check. The DAD check tests IP addresses by sending a neighbor solicitation to each IP address it checks. If another device replies to the neighbor solicitation, a duplicate IP address is detected.

If a duplicate address is detected, the IP interface remains or becomes inactive, and a warning message is logged. If no duplicate address is detected, the IP interface transitions to or remains in the active state. The switch does not automatically repeat the DAD check after the first check is complete. To manually run a DAD test on an interface or IP address, enter the run ipv6 dad command.

Because the automatic DAD check only runs when an interface is initialized, the switch does not detect a duplicate IP address if that address becomes active after the switch interface is initialized. However, if the switch is rebooted or the interface in brought down and then up, the automatic DAD check runs and sets to inactive any interface for which a duplicate IP address is detected.

To successfully test an IPv6 interface, at least one port in the host VLAN must be in the Up state. If all ports in the host VLAN are Down, the DAD check does not run. If a port is later added to the host VLAN, or if a port in the host VLAN transitions to Up after the DAD check at initialization is complete, a duplicate IP address can be detected and logged, but the IP interface on the host VLAN remains active.