Configuring Duplicate Address Detection

Duplicate address detection is a process in which a device checks whether the address to be used for an interface has been used by another interface.

Usage Scenario

Before configuring an IPv6 unicast address for an interface, check all the interfaces on the local link and ensure that the IPv6 unicast address is unique and is not used by another interface.

Pre-configuration Tasks

Before configuring duplicate address detection, complete the following tasks:

Connect interfaces and configure physical parameters for the interfaces to ensure that the physical status of the interfaces is Up.
Configure link layer protocol parameters for the interfaces to ensure that the link layer protocol status of the interfaces is Up.
Configure IPv6 addresses for interfaces.

Setting the Number of Duplicate Address Detection Attempts: A device can send NS messages to detect whether the IPv6 address to be configured has been used by another device. Therefore, the number of duplicate address detection attempts refers to the number of times NS messages are sent. Duplicate address detection is implemented using NS and NA messages. Duplicate address detection is implemented in a similar way as gratuitous ARP in IPv4.

Setting the Duplicate Address Detection Interval: A device can send NS messages to detect whether its neighbors are reachable. Therefore, you can set the NS message transmission interval to control the neighbor reachability detection frequency. Frequent sending of NS messages can immediately determine whether neighbors are reachable. It, however, degrades the performance of the device. Therefore, it is recommended that the interval not be set too short.

Setting a Timeout Period for DAD Messages: If many VLANs are configured on a VLAN tag termination sub-interface, DAD messages may fail to be transmitted within the default timeout period (1s). To resolve this issue, run the ipv6 nd dad timeout command to prolong the timeout period for DAD messages.

Disabling DAD from Continuing Detection in an Address Conflict Scenario

Configuring a Limit on the Rate at Which NS Messages Are Sent for DAD to Continue Detection in an Address Conflict Scenario

Configuring a Threshold for DAD to Consider an Address Available in an Address Conflict Self-Recovery Scenario

Verifying the Configuration of Duplicate Address Detection: After configuring duplicate address detection, verify the configuration.