I the only source of Internet connection I have currently is my phone. I wanted to share this network with other systems, via a lan/wireless router. So here is a basic setup:
Setting up Internet gateway: Laptop + Android Phone
I connected Android Phone via USB cable to the laptop and enabled USB thether, so I have a usb device /dev/usb0. This was automatically detected by Network Manager. Also I connected Laptop to the router via a LAN.
I setup the NAT on my Laptop using this script as follows:
# cat nat.sh IFOUT=usb0 IFLAN=em1 echo 1 > /proc/sys/net/ipv4/ip_forward && sudo iptables -t nat -A POSTROUTING -o $IFOUT -j MASQUERADE && sudo iptables -A FORWARD -i $IFOUT -o $IFLAN -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT && sudo iptables -A FORWARD -i $IFLAN -o $IFOUT -j ACCEPT
So all I had to do to setup is do this:
# sh nat.sh
And IPTABLES take care of masquerading the IP addresses to-and-fro from local network to the internet. I received IP address 192.168.1.2 for the Laptop, which becomes a default gateway for rest of the machines connected to the router.
Setting up Internet user: Desktop machine
Now on the desktop machine ( with IP address 192.168.1.3 ), I only had to setup the routes and DNS server:
# route add default gw 192.168.1.2 # route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 192.168.1.2 0.0.0.0 UG 0 0 0 em1 0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 em1 192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 em1 # cat /etc/resolv.conf # Generated by NetworkManager #nameserver 192.168.1.3 nameserver 188.8.131.52 nameserver 184.108.40.206 nameserver 192.168.42.129
Thats all, that was needed. I had done the NAT + MASQUERADE setup earlier, however it was on Fedora Core 2 and some commands didn’t match up, esp. how to use conntrack module.