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How to make sense of an iptables chain configuration

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linux-howto

http://unix.stackexchange.com – This is about how to make sense of the chains found in the iptables default configuration on a typical home router running OpenWrt (a stripped down Linux for router devices), but which ultimately may not be specific to that particular system. Let's focus on the INPUT main chain here, and disregard FORWARD and OUTPUT from the same table, as well as PREROUTING and POSTROUTING from the nat table. Doing an iptables -L -t filter shows a large number of rules. I have rearranged the output below to make it less intimidating, and in an attempt to pinpoint the parts that hamper my understanding. The (HowTos)