[lug] the world's easiest iptables firewall

Joshua Rubin joshua at cybertron.cc
Mon Dec 13 16:06:49 MST 2004

On Monday 13 December 2004 03:35 pm, David Anselmi wrote:
> Jeffrey Siegal wrote:
> > Kevin Fenzi wrote:
> >> Optionally, you can add in between these 2 rules:
> >> iptables -A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
> >
> > I prefer to use "-m state --state NEW" or --syn for that.  Other packets
> > should be allowed only for existing connections.
> Has to be NEW,ESTABLISHED doesn't it?
> Dave
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iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A INPUT -m state --state NEW -p tcp --dport 22 -j ACCEPT
iptables -A INPUT -d -i lo -j ACCEPT
iptables -A INPUT -j DROP
iptables -A FORWARD -j DROP

ESTABLISHED is taken care of in the first rule.

I added the loopback interface to this as well. The kernel automatically 
filters out everything not originating from the loopback with netmask (no loopback spoofing), this rule makes sure that no loopback 
traffic is blocked. I also drop all forwarding as another precaution.


Joshua Rubin
Joshua.Rubin at Colorado.EDU
(303) 909-6199


Cassini Mission to Saturn
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