问题：
$ dmesg
[ 1944.889305] IPv6: enp12s0f1: IPv6 duplicate address fe80::8043:7fff:9295:aeb7 detected!
[ 1989.849200] IPv6: enp12s0f1: IPv6 duplicate address fe80::190:f9da:91b9:5499 detected!
[ 1989.977194] IPv6: enp12s0f1: IPv6 duplicate address fe80::39cc:d861:cc0c:ae05 detected!
[ 1990.361173] IPv6: enp12s0f1: IPv6 duplicate address fe80::8043:7fff:9295:aeb7 detected!
$ ifconfig
会出现三个MAC地址
解决：
1.临时改变可以修改下面文件：/proc/sys/net/ipv6/conf/enp12s0f1/accept_dad
把accept_dad的值改为０，重启后会失效
2.修改/etc/sysctl.d/下的配置文件如下：
$ sudo vim 90-local.conf
net.ipv6.conf.all.accept_dad = 0
net.ipv6.conf.default.accept_dad = 0
参考：
http://blog.csdn.net/crazyhacking/article/details/8561387
https://criticalindirection.com/2015/06/30/ipv6_dad_floating_ips/