The output can give you information
about any problems with the rules you have set up. Periodically check the /var/log/messages
file to see if anyone has tried to intrude on any of your ports.
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Running a Linux Firewall/Router 18
To find out more about how Shorewall works to configure your iptables firewalls, refer to the
Shorewall Web site (www.shorewall.net). You can still use iptables commands to view the current
firewall (iptables -L) or temporarily flush your firewall (iptables -F). However, other
changes you might make with iptables will be temporary because the next time you reboot,
Shorewall will take over again.
Using Firewalls with iptables
Understanding how iptables works will help you with any firewall you have configured in a Linux
system. Previous firewall features??”ipchains and ipfwadm??”are no longer included in the Linux
kernel. Unless you are using a Linux with an older kernel (which only a few floppy firewall distributions
still have), iptables is your primary tool for firewall configuration in Linux.
The commands used to configure iptables are not very intuitive. Using the iptables command,
you add rules (one by one) to your running Linux kernel. When you have a set of rules you like,
save those rules to a file using iptables-save.
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