Install filtergen by entering the following commands in the terminal:
sudo apt update sudo apt install filtergen
Description:
packet filter generator for various firewall systems
filtergen is a packet filter generator. It compiles a fairly high-level description language into iptables, ipchains, or ipfilter scripts (and has bits of support for Cisco IOS access lists).
Homepage: http://spacepants.org/src/filtergen/
Version: 0.12.8-1
Section: universe/net