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Old 01-09-2003, 01:21 AM   #1
Registered: Dec 2001
Posts: 35

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how packets traverse thru iptables chains?

As above. I'm confused with how the chains are traversed in iptables.

Let's say the Linux box has 3 NIC: eth0 for internet, eth1 for DMZ and eth2 for local LAN.

When a box in LAN trying to access a webserver in the internet, would the packet go through INPUT chain, as in the case of using ipchains? And what happen then?

Currently I believe it will go straight to FORWARD chain and then SNAT'ed in the POSTROUTING chain. So, there's no INPUT or OUTPUT chains involved.

Is this true? This is what I can grasp from IPTables Tutorial. But when I read some firewall examples, it filters the INPUT chain too...
Old 01-09-2003, 01:50 AM   #2
Registered: Dec 2001
Posts: 35

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Hm... After another reading of the book Linux Firewall, seems that the correct path is NOT to traverse INPUT and OUTPUT chain when the packet is not to/from localhost (i.e. firewall itself).


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