Disabling BIND9 IPv6 on Debian 8.0 / Ubuntu LTS 16.04
If you use BIND and your system is not configured to use IPv6 then you will see the following annoying messages in your /var/log/syslog file:
named: error (network unreachable) resolving 'uk/DS/IN': 2001:500:1::803f:235#53
To resolve this you need to pass the "-4" option to /usr/sbin/named daemon.
The bind9 package historically used the /etc/default/bind9 file to allow you to configure custom options for the service.
However, Debian Jessie now uses systemd and because, unfortunately, the bind9 package maintainers did not do a good job adapting to this change, your only option for the time being seems to be to edit the /lib/systemd/system/bind9.service file to add the "-4" option and then run:
systemctl daemon-reload service bind9 restart
It is possible that this process will need to be repeated if bind9 package is updated.
Similar instructions apply to Ubuntu LTS 16.04.