47: eth0.5@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master red state UP group default qlen 1000 link/ether 00:00:00:00:07:ec brd ff:ff:ff:ff:ff:ff inet 192.0.2.121/28 brd 192.0.2.127 scope global eth0.5 valid_lft forever preferred_lft forever inet6 2001:db8:200:f0::114/64 scope global dadfailed tentative valid_lft forever preferred_lft forever inet6 fe80::0:0:fe53:7ec/64 scope link valid_lft forever preferred_lft forever
IPv6 unicast address shows dadfailed
From Kernel docs:
accept_dad - INTEGER Whether to accept DAD (Duplicate Address Detection). 0: Disable DAD 1: Enable DAD (default) 2: Enable DAD, and disable IPv6 operation if MAC-based duplicate link-local address has been found.
https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt