Simulating windows firewall with iptables

lets simulate Windows XP firewall with iptables.The built-in firewall on windows XP is enabled by default with service pack 2 or better. The standard configuration is to allow outbound connections from the host system, and deny inbound connections unless they are explicitly configured. The windows firewall also allows any traffic that is a reply to traffic that the host originally generated outbound. After you execute the iptables -F command to flush out all of the previously configured rules, the following commands would configure the Linux host similarly:

iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -A INPUT -m state –state ESTABLISHED,RELATED -j ACCEPT
The –state extension track the current status of the connections. By specifying ESTABLISHED or RELATED, the firewall allows packets that are part of a currently established session, or packets that are starting a new session, but where the session is related to an existing session (such as FTP data session). If you were hosting a service on this system, such as a web server, you would need to configure the INPUT chain appropriately. This configuration would afford any Linux system a minimum level of firewall security with virtually no impact to its overall functionality.


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