Table of Contents Introduction Enabling knockd Port-knocking Open the port Close the port Using Hping3 / Nmap Open the port Close the port Alternatives Introduction Port-knocking is a stealth method to open ports that the firewall keeps closed by default. A port-knock server listens to all traffic on an ethernet (or PPP) interface, looking for a special “knock” sequences of port-hits.

Table of Contents Iptables UFW Manage ufw by predefined service names Extended syntax Reorders firewall rules Iptables List the configured rules: # iptables -L # iptables -L -t nat iptables contains 5 tables, (-t, --tables): raw, filter, nat, mangle and security. In common use cases, filter and nat is used, where filter is associated with the firewall and nat is used for network address translation such as port forwarding.