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Old 04-21-2009, 10:08 AM   #1
Registered: May 2004
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Iptables: prevent spoofing with multiple internal nets?

Hi all,

I want to prevent spoofing in my iptables config. However, I am confused about how to go about it when using multiple internal nets. For instance:


So, to do anti-spoofing I have to put a line like:

iptables -A FORWARD -i eth1 -s ! (NET_1 OR NET_2) -j DROP

Obviously the above line won't work in iptables, but you see what I am trying to accomplish. Can anyone help me out?
Old 04-21-2009, 11:12 AM   #2
Registered: Feb 2009
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Create a rule for each single network?
Old 04-21-2009, 01:36 PM   #3
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iptables -P FORWARD DROP
iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i eth1 -o eth0 -s -m state --state NEW -j ACCEPT
iptables -A FORWARD -i eth2 -o eth0 -s -m state --state NEW-j ACCEPT


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