This configuration assumes the following on your firewall computer:

• The network card IP is 192.168.1.2
• ppp0 is your mobile modem

1. Enable IP forwading

   1. # vi /etc/sysctl.conf

   2. Find

      net.ipv4.ip_forward = 0

   3. Change to:

      net.ipv4.ip_forward = 1

   4. # echo 1 > /proc/sys/net/ipv4/ip_forward

   5. # service network restart

2. Enable IP masquerading

   1. # service iptables stop

   2. # iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE

   3. # service iptables save

   4. # service iptables restart

3. Assign the IP address of the firewall computer to the gateway of the computers on the network.
   1. Go to the client computer

   2. # vi /etc/sysconfig/network-scripts/ifcfg-eth0

   3. Add this line:

      GATEWAY=192.168.1.2

For Window computers, change Default gateway in the Internet Protocol(TCP/IP) to 192.168.1.2