```
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