Listet auf, welche Ports man für welche Services (DNS, HTTP, SMTP, POP, IMAP, FTP, etc.) wie (intern, extern und Range) offen haben muss, damit der Service funktioniert.
The following is an example iptables firewall that allows incoming ssh connections from an individual IP address (192.168.1.100), allows all outbound traffic, and uses stateful inspection.
ate-limit all incoming SSH connections to 8 in a one minute window. Normal users will have no trouble logging in, but the brute force attacks will be dropped, limiting the number of possible account combinations from unlimited, to 8.