vi /etc/network/interfaces
iface vmbr0 inet6 dhcp
accept_ra 2
request_prefix 1
vi /etc/sysctl.conf
net.ipv6.conf.all.accept_ra=2
net.ipv6.conf.default.accept_ra=2
net.ipv6.conf.vmbr0.accept_ra=2
net.ipv6.conf.all.autoconf=1
net.ipv6.conf.default.autoconf=1
net.ipv6.conf.vmbr0.autoconf=1