In case you want to supply answwers when installing package, here's how you can find wich one are needed by the package:
apt-get install iptables-persistentapt-get install debconf-utils debconf-get-selections | grep ^iptables-persistentecho "iptables-persistent iptables-persistent/autosave_v6 boolean true" | debconf-set-selections apt-get install iptables-persistent