iptables: what is a chain?

Question

I've been reading about iptables for hours and I still don't understand what is it that they're calling a "chain". I see this word everywhere in the doc and in tutorials and it's still fuzzy to me what they're talking about. What's a chain?

Answer 1

Chain is nothing but sequence of filter rules maintained by iptables.

• INPUT Chain : For packets coming into the system or destined for the system.
• FORWARD Chain : For packets travelling (being routed) through the system.
• OUTPUT Chain : For packets leaving the system or originating from the system.

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