iptables is a linux application that allows you to configure the built-in linux firewall. There are abstraction layers built on top of it, including nice GUIs, but I recently had some very basic rules I wanted to implement, and figured I'd learn how to do it directly in iptables. It turned out to be easy to configure, and I thought I'd give a very basic introduction. First though, I relied on the ubuntu documentation to get up and running ( https://help.ubuntu.com/community/IptablesHowTo ). I'll pretty much just regurgitate what's in there - I've said it before, stop believing that linux documentation is written only for people who already know linux. Also, depending on your setup, most of these commands might require elevation (sudo). By default, iptables defines three rule chains: INPUT , FORWARD and OUTPUT . We'll only concern ourselves with INPUT - namely the chain used for incoming packets directed at this particular machine. At any point, you can list the rules by entering iptables -L . If listing the rules turns out to be really slow, try using iptables -L -n . The -n option means that the display will output IP addresses and ports in numeric format, without trying to do a DNS lookup. If the -n option Read More...

Read the complete post at http://feedproxy.google.com/~r/CodeBetter/~3/rHaPF71cZnU/an-introduction-to-iptables.aspx

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Posted Wed, Feb 3 2010 12:36 PM by DDD Feeds