Firewall script

A script for quickly set up firewall rules on linux for either an iptables or nftables backend

Tested on Debian 12, CentOS 9, Rocky 8/9

All testing has been done with distributions using nftables, so there potentially could be issues with the iptables backend

Usage: ./firewall.sh [-p] [-d policy] [-f firewall] [-r port,action,direction[,ip[,protocol]]] [-s] [-S ip] [-n] [-N ip] [-i] [-y] [-b]
  -r	Rule to set, with the actions: "accept" or "drop", the directions: "in" or "out", and the protocols: "tcp", "udp".
    	If the port is "_", then the rule applies to all ports
  -p	Save rules persistently (restore after reboot)
  -d	Set default firewall policy to actions: "accept" or "drop"
  -f	Use specific firewall instead of attempting autodetection
  -S	Allow incoming ssh from specific ip
  -s	Allow incoming ssh from any ip
  -N	Allow dns to specific ip
  -n	Allow dns to any ip
  -i	Allow icmp pings
  -y	Don't confirm connectivity
  -b	Don't back up previous rules

Examples:
  ./firewall.sh -f iptables -r 80,accept,in -r 443,accept,in -r 22,drop,out
  ./firewall.sh -f nftables -d drop -S 192.168.1.2 -N 8.8.8.8
  ./firewall.sh -r 1234,accept,in,192.168.1.2