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Tue, 21 Jun 2011

/Admin/iptables: Build A Basic Firewall with iptables

This seems like a good starting point[1], blocking everything except SSH, established, loopback, and outgoing connections:

iptables -P INPUT ACCEPT
iptables -F
iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j ACCEPT
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT ACCEPT
iptables -L -v
/etc/init.d/iptables-persistent save

On my Debian system, the last "save" line puts a reloadable copy of the current running iptables rules in /etc/iptables/rules.v4 & /etc/iptables/rules.v6. Thereafter, it is also possible (advisable?) to edit these files directly to add/modify rules. For instance to open up the http port, add the following line to /etc/iptables/rules.v4:

-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT

Then load the new ruleset using:

iptables-restore < rules.v4

[1] http://wiki.centos.org/HowTos/Network/IPTables

posted at: 04:56 | path: /Admin/iptables | permanent link to this entry

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Tue, 21 Jun 2011