Restoring the deleted rules

When I used the iptables -D commands, I only deleted the rules from the runtime configuration, and not from the rules.v4 configuration file. To restore the rules that I deleted, I can either reboot the machine or restart the netfilter-persistent service. The latter choice is quicker, so I'll activate this with the following code:

donnie@ubuntu:~$ sudo systemctl restart netfilter-persistent
[sudo] password for donnie:
donnie@ubuntu:~$

The iptables -L and iptables -t mangle -L commands will show that all the rules are now back in effect.