Yes, by default is not working and you may get no global ipv6 address.
In your /etc/rc.local add the following:
dhclient -6 ${INTERFACE};
You can manually test the command in advance and check that actually your are getting a global ipv6 address
sudo apt-get install isc-dhcp-client
service ipv6-dhclient status
/sbin/dhclient ${INTERFACE};
https://wiki.ubuntu.com/DHCPv6
https://documentation.online.net/en/dedicated-server/network/ipv6/prefix#traffic_limitation_of_your_client
outime/ipv6-dhclient-script#7
https://manpages.debian.org/jessie/isc-dhcp-client/dhclient.8.en.html
https://github.com/outime/ipv6-dhclient-script/blob/master/ipv6-dhclient-script.sh
https://wiki.debian.org/NetworkConfiguration
http://www.tldp.org/HOWTO/Linux+IPv6-HOWTO/ch03s02.html#idp50485632
http://www.ruwenzori.net/ipv6/Jims_LAN_IPv6_global_connectivity_howto.html