Internet Sharing In Linux

Enable IP forwarding Run as root sysctl -w net.ipv4.ip_forward=1

To enable it in system startup, edit the file /etc/sysctl.conf and set net.ipv4.ip_forward = 1

iptables Run command as root iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE service iptables save

Configuration The configuration should be like this

Router Connected to the internet provider IP : 192.168.1.1

Internet Connected System eth0 (LAN Card 1) Connected to router • • •

IP : 192.168.1.10 Netmask : 255.255.255.0 Gateway : 192.168.1.1 (IP of the router)

eth1 (LAN Card 2) Connected to the other system • • •

IP : 192.168.0.20 (Not the same network as the first card) Netmask : 255.255.255.0 Gateway : 192.168.1.1 (IP of the router)

Second System

LAN Card connected to the first system • • •

IP : 192.168.0.30 Netmask : 255.255.255.0 Gateway : 192.168.0.20 (IP of the second Card in the first system)

Status Some results of various commands are shown here. Check to see if it matches the result on your system. # iptables -t nat -L POSTROUTING Chain POSTROUTING (policy ACCEPT) target prot opt source MASQUERADE all -- anywhere # cat /proc/sys/net/ipv4/ip_forward 1 # iptables -L Chain INPUT (policy ACCEPT) target prot opt source

destination anywhere

destination

Chain FORWARD (policy ACCEPT) target prot opt source

destination

Chain OUTPUT (policy ACCEPT) target prot opt source

destination