After upgrade of Turris OS to 3.7 which brings the guest network functionality to Foris I noticed that this guest network is not issuing IPv6 addresses to clients. I achieved this by following these steps.
In order to advertise IPv6 addresses to guest clients I had to add two firewall rules (in /etc/config/firewall):
config rule
option target 'ACCEPT'
option family 'ipv6'
option src 'guest_turris'
option proto 'icmp'
option name 'Allow guest ICMP input'
config rule
option enabled '1'
option target 'ACCEPT'
option src 'guest_turris'
option family 'ipv6'
option proto 'udp'
option dest_port '546-547'
option name 'Allow Guest DHCPv6'
In /etc/config/network file add these two rows in config interface 'guest_turris' section:
option ip6assign '64'
option ip6hint 'ffff'
And finally in /etc/config/dhcp in guest pool (section config dhcp 'guest_turris') add these rows
option ra 'server'
option ra_management '0'
And after router's reboot guests should be receiving IPv6 addresses too.
BTW instead of full router's reboot, it should be enough to restart:
/etc/init.d/network restart /etc/init.d/firewall reload /etc/init.d/odhcpd restart