iptables --flush # Flush all the rules in filter and nat tables
iptables --table nat --flush
iptables --delete-chain
# Delete all chains that are not in default filter and nat table
iptables --table nat --delete-chain
echo 1 > /proc/sys/net/ipv4/ip_forward
# Set up IP FORWARDing and Masquerading
iptables --table nat --append POSTROUTING --out-interface eth0 -j MASQUERADE
iptables --append FORWARD --in-interface eth1 -j ACCEPT
# Forward packets that are part of existing and related connections from eth0 to eth1.
#
iptables -A FORWARD -i eth0 -o eth1 -m state --state ESTABLISHED,RELATED -j ACCEPT
#
# Permit packets in to firewall itself that are part of existing and related connections.
#
iptables -A INPUT -i eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -i eth1 -s 0/0 -d 0/0 -j ACCEPT
iptables -A INPUT -i lo -s 0/0 -d 0/0 -j ACCEPT