1-16
IPv6 Addressing Configuration
Duplicate Address Detection (DAD)
Operating Notes
■ A verified link-local unicast address must exist on a VLAN interface before
the switch can run DAD on other addresses associated with the interface.
■ If a previously configured unicast address is changed, a neighbor adver-
tisement (an all-nodes multicast message--ff02::1) is sent to notify other
devices on the VLAN and to perform duplicate address detection.
■ IPv6 addresses on a VLAN interface are assigned to multicast address
groups identified with well- known prefixes. For more on this topic, refer
to “View IPv6 Gateway, Route, and Router Neighbors ” on page 1-25.
■ DAD is performed on all stateful, stateless, and statically configured
unicast addresses.
■ Neighbor solicitations for DAD do not cause the neighbor cache of
neighboring switches to be updated.
■ If a previously configured unicast address is changed, a neighbor adver-
tisement is sent on the VLAN to notify other devices, and also for duplicate
address detection.
■ If DAD is disabled when an address is configured, the address is assumed
to be unique and is assigned to the interface.
Syntax:. ipv6 nd reachable-time < milliseconds >
Used on VLAN interfaces to configure the length of time in
milliseconds a neighbor will be considered reachable after the
Neighbor Unreachability Detection algorithm has confirmed
it to be reachable. When the switch operates in host mode, this
setting can be overridden by a reachable time received in a
router advertisement.
This value can be configured in a router advertisement to help
ensure that all hosts on a VLAN are using the same reachable
time in their neighbor cache. Refer to “Neighbor Discovery
(ND)” on page 1-12.
To view the current setting, use show ipv6 nd.
Range: 1000 - 2147483647 ms; Default: 30000 ms.
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