Ubuntu 16.04 doesn't have Fail2Ban 0.10.x in the distribution repositories, so if you want the newer version with IPv6 support you'll have to do the upgrade manually. Here's how to install Fail2Ban 0.10 on Ubuntu 16.04.
Backup existing settings and remove Fail2Ban completely
service fail2ban stop cp -a /etc/fail2ban/ /etc/fail2ban_backup/ apt-get remove --auto-remove fail2ban apt-get purge --auto-remove fail2ban rm -r /etc/fail2ban/
Download the newer version and install it manually
At the time of writing the latest version is 0.10.4, but you may want to check the release page in case there's a newer one.
wget https://github.com/fail2ban/fail2ban/archive/0.10.4.tar.gz tar xzf 0.10.4.tar.gz cd fail2ban-0.10.4/ python setup.py install
Put Ubuntu-specific files into place
cp files/bash-completion /etc/bash_completion.d/fail2ban cp man/*.5 /usr/share/man/man5 cp man/*.1 /usr/share/man/man1 wget -O /etc/logrotate.d/fail2ban https://raw.githubusercontent.com/fail2ban/fail2ban/debian/debian/fail2ban.logrotate cp build/fail2ban.service /lib/systemd/system/fail2ban.service systemctl enable fail2ban service rsyslog restart
Import your old settings
This will vary depending on your configuration. Consider any changes you made in the backup files at /etc/fail2ban_backup. For example, if you adjusted dbpurgeage in fail2ban.conf you'll want to modify the new file the same. Or if you set up custom filters in filter.d/ or jails in jail.d/ you should copy the files to match. Once that's done it should be okay to simply copy the jail.local file over.
cp /etc/fail2ban_backup/jail.local /etc/fail2ban/jail.local
Start it up!
You may want to monitor /var/log/fail2ban.log while you do this with
tail -f /var/log/fail2ban.log in another terminal.
service fail2ban start service fail2ban status fail2ban-client version
Provided there are no errors you should be good to go with Fail2Ban 0.10 with IPv6 support on Ubuntu 16.04!