Configuring IPv6 Duplicate Address Detection
During the stateless autoconfiguration process, duplicate address detection verifies the uniqueness of new unicast IPv6 addresses before the addresses are assigned to interfaces (the new addresses remain in a tentative state while duplicate address detection is performed). Duplicate address detection is performed first on the new link-local address. When the link local address is verified as unique, then duplicate address detection is performed all the other IPv6 unicast addresses on the interface.
Duplicate address detection is suspended on interfaces that are administratively down. While an interface is administratively down, the unicast IPv6 addresses assigned to the interface are set to a pending state. An interface returning to an administratively up state restarts duplicate address detection for all of the unicast IPv6 addresses on the interface.
When a duplicate address is identified, the state of the address is set to DUPLICATE, the address is not used, and the following error message is generated:
%PIX|ASA-4-325002: Duplicate address ipv6_address/MAC_address on interface
If the duplicate address is the link-local address of the interface, the processing of IPv6 packets is disabled on the interface. If the duplicate address is a global address, the address is not used. However, all configuration commands associated with the duplicate address remain as configured while the state of the address is set to DUPLICATE.
If the link-local address for an interface changes, duplicate address detection is performed on the new link-local address and all of the other IPv6 address associated with the interface are regenerated (duplicate address detection is performed only on the new link-local address).
The security appliance uses neighbor solicitation messages to perform duplicate address detection. By default, the number of times an interface performs duplicate address detection is 1.
To change the number of duplicate address detection attempts, enter the following command:
hostname(config-if)# ipv6 nd dad attempts value
The value argument can be any value from 0 to 600. Setting the value argument to 0 disables duplicate address detection on the interface.
When you configure an interface to send out more than one duplicate address detection attempt, you can also use the ipv6 nd ns-interval command to configure the interval at which the neighbor solicitation messages are sent out. By default, they are sent out once every 1000 milliseconds.
To change the neighbor solicitation message interval, enter the following command:
hostname(config-if)# ipv6 nd ns-interval value
The value argument can be from 1000 to 3600000 milliseconds.
Note Changing this value changes it for all neighbor solicitation messages sent out on the interface, not just those used for duplicate address detection.
Continue reading here: Configuring IPv6 Default and Static Routes
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