# Configuration on the gateway:
#eth0 to external network (WAN)
#eth1 to internal network (LAN)
# Probably already set by ISP
ifconfig eth0 XXX.XXX.XXX.XXX netmask 255.255.255.0 broadcast XXX.XXX.XXX.255
# ifconfig eth1 192.168.10.101 will probably set the rest correctly by default
ifconfig eth1 192.168.10.101 netmask 255.255.255.0 broadcast 192.168.10.255
# Delete and flush. Default table is "filter". Others like "nat" must be explicitly stated.
iptables --flush
iptables --table nat --flush
iptables --delete-chain
iptables --table nat --delete-chain
# Set up IP FORWARDing and Masquerading
iptables --table nat --append POSTROUTING --out-interface eth0 -j MASQUERADE
iptables --append FORWARD --in-interface eth1 -j ACCEPT
echo 1 > /proc/sys/net/ipv4/ip_forward # Enables packet forwarding by kernel
# (didn't need this for only one box, in my experience)
# Create a route for internal packets:
route add -net 192.168.10.0 netmask 255.255.255.0 gw XXX.XXX.XXX.XXX dev eth1