Linux Networking Cookbook

Setting up a firewall with IPtables

We touched upon iptables a little while discussing NAT, but now we're going to go a bit deeper into configuring a secure firewall for your network.

How to do it…

A properly configured firewall should be configured in a default deny configuration with specific allows (Whitelist) for what you want to accept:

# 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 -A FORWARD -i eth0 -j ACCEPT
# iptables -t nat -A POSTROUTING -o eth2 \
-j MASQUERADE
# iptables -A FORWARD -i eth2 -o eth0 -m \
state --state RELATED,ESTABLISHED -j ...