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I have a Dual PC setup. Two PC's are networked together via crossover cable. The Windows PC is running Windows 7 SP1 64-bit and the Linux PC is running Slackware 14 64-bit with iptables.

My firewall and routing is essentially:

{DROP All protocols and ports}
{ACCEPT specific protocols and ports}

# Rules to route from Windows PC to Linux PC
$IPTABLES -A INPUT -i eth1   -s 192.168.1.10   -m state --state NEW  -j ACCEPT
$IPTABLES -A FORWARD -i eth1   -s 192.168.1.10   -m state --state NEW  -j ACCEPT
$IPTABLES -A FORWARD -o eth1   -s 192.168.1.10   -m state --state NEW  -j ACCEPT
$IPTABLES -t nat -A POSTROUTING -o eth0   -s 192.168.1.10  -j MASQUERADE
echo 1 > /proc/sys/net/ipv4/ip_forward


{DROP everything not contained in any of the above rules}

Assuming that the Windows PC is virus-free and/or hypothethically invulnerable to viruses/trojans/backdoors etc., how secure would the Windows PC be with a properly set up Linux firewall?

Would the Windows PC still need a firewall?

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2 Answers 2

up vote 2 down vote accepted

In the scenario you describe, your Linux box is essentially acting as a network firewall for your Windows machine. So your question basically boils down to "Do I need a host-based firewall if I am already using a network firewall?"

The answer to that question is no, you don't need one. However, it would be helpful to use one. See the concept of Defense in depth.

A good explanation on what host-based firewalls can do compared to network firewalls can be found in this question.

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Security isn't a state, it's a progress. A firewall is important, but I think: virus detection on windows is a good idea, and the firewall before the windows pc too. But I would install the Windows firewall too, because you can blog programs. iptables doesn't know which program wants connect to the internet. So my oppinion: Use both firewalls.

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