ping6 DAD problem

If this error messages appears

ping6 cannot assign requested address

and dmesg yields something along

[ 411.224402] IPv6: eth0: IPv6 duplicate address fe80::dead:beef detected!

then a possible solution is to disable duplicate address discovery (DAD). Add the following line in /etc/sysctl.conf.

net.ipv6.conf.eth0.accept_dad=0