Use the ipv6 nd dad attempts command in Interface Configuration mode to configure the number of consecutive neighbor solicitation messages that are sent
on an interface while duplicate address detection is performed on the Unicast IPv6 addresses of the interface.
To return the number of messages to the default value, use the no form of this command.
ipv6 nd dad attempts value
no ipv6 nd dad attempts
Interface Configuration mode
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
uses neighbor solicitation messages to verify the uniqueness of Unicast IPv6 addresses.
The DupAddrDetectTransmits node configuration variable (as specified in RFC 4862, IPv6 Stateless Address Autoconfiguration)
is used to automatically determine the number of consecutive neighbor solicitation messages that are sent on an interface,
while duplicate address detection is performed on a tentative Unicast IPv6 address.
The interval between duplicate address detection, neighbor solicitation messages (the duplicate address detection timeout
interval) is specified by the neighbor discovery-related variable RetransTimer (as specified in RFC 4861, Neighbor Discovery
for IPv6), which is used to determine the time between retransmissions of neighbor solicitation messages to a neighbor when
resolving the address or when probing the reachability of a neighbor. This is the same management variable used to specify
the interval for neighbor solicitation messages during address resolution and neighbor unreachability detection.
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. Duplicate address detection is automatically
restarted on an interface when the interface returns to being administratively up.
An interface returning to administratively up, restarts duplicate address detection for all of the Unicast IPv6 addresses
on the interface. While duplicate address detection is performed on the link-local address of an interface, the state for
the other IPv6 addresses is still set to TENTATIVE. When duplicate address detection is completed on the link-local address,
duplicate address detection is performed on the remaining IPv6 addresses.
When duplicate address detection identifies a duplicate address, the state of the address is set to DUPLICATE and the address
is not used. If the duplicate address is the link-local address of the interface, the processing of IPv6 packets is disabled
on the interface and an error SYSLOG message is issued.
If the duplicate address is a global address of the interface, the address is not used and an error SYSLOG message is issued.
All configuration commands associated with the duplicate address remain as configured while the state of the address is set
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).
Note. Since DAD is not supported on NBMA interfaces the command is allowed but does not impact on an IPv6 tunnel interface of the
ISATAP type it does not impact. The configuration is saved and will impacted when the interface type is changed on another
type on which DAD is supported (for example, to the IPv6 manual tunnel).
The following example configures five consecutive neighbor solicitation messages to be sent on VLAN 1 while duplicate address
detection is being performed on the tentative Unicast IPv6 address of the interface. The example also disables duplicate address
detection processing on VLAN 2.
switchxxxxxx(config)# interface vlan 1
switchxxxxxx(config-if)# ipv6 nd dad attempts 5
switchxxxxxx(config)# interface vlan 2
switchxxxxxx(config-if)# ipv6 nd dad attempts 0