I'm studying iptables and am getting confused on the difference between FORWARD and OUTPUT chains. In my training documentation, it states:
If you're appending to (-A) or deleting from (-D) a chain, you'll want to apply it to network data traveling in one of three directions:
- INPUT - All incoming packets are checked against the rules in this chain.
- OUTPUT - All outgoing packets are checked against the rules in this chain.
- FORWARD - All packets being sent to another computer are checked against the rules in this chain.
This confuses me because, in my mind, packets leaving for a host WOULD be outgoing. So are there scenarios where a packet would be going to another computer but NOT be "outgoing"? How would iptables distinguish between the two?