[Bradford] IPv6 - again

[Devo Too]

Hi Folks,

When upgrading from Debian8 to Debian9 something went wrong (or was 
deliberately preserved by the system) on my remote server. Systemd 
wasn't installed completely, leaving /etc/systemd/network/ empty. No 
other omissions noted but it's early days yet.

Instead I have the Jessie throwback /etc/network/interfaces which has 
this for IPv6, in a block below the IPv4 static configuration:

#IPV6 static configuration
#       iface eth0 inet6 static
#       pre-up modprobe ipv6
#       address 2001:xxxx:xxxx:xxx:0000:0000:0002
#       netmask 64
#       gateway 2001:xxxx:xxxx:xxxx:xxxx:0000:0000:0001
# END IPV6 configuration

which, to my untrained eye, looks perfectly good and proper.

Questions:

1. If I simply uncomment this block is there more to do?

2. Is this the right way to go in the first place, or should I try to 
patch up Systemd? (calm down, David, I'm only asking for a working way 
forward which will withstand the next update or upgrade!) ;-)

Any sysadmins out there reading this?

TIA

Mike