====== Quick Links ======
  * http://os.51cto.com/art/201103/249341.htm
  * http://www.xuebuyuan.com/1945506.html
  * http://blog.csdn.net/wbryfl/article/details/6146617
  * http://www.ahlinux.com/safe/16121.html
  * http://linux.alai.net/viewblog.php?id=41605

====== Setup Gateway ======
  * Edit /etc/network/interfaces
<code>
 This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
allow-hotplug eth0
iface eth0 inet dhcp

# The secondary network interface
iface eth1 inet static
address 192.168.0.1
netmask 255.255.255.0
</code>

  * Restart networking
<code>
# This does not work: /etc/init.d/networking restart
sudo ifdown eth1 && sudo ifup eth1
</code>

  * Enable ip forward: edit /etc/sysctl.conf, uncomment "#net.ipv4.ip_forward=1".
<code>
### OLD
#net.ipv4.ip_forward=1

### NEW
net.ipv4.ip_forward=1
</code>

  * Now we should be alble to ping 192.168.0.1. To ping 166.111.142.1, we should do
<code>
 iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -o eth0 -j MASQUERADE
</code>

  * Set up DHCP server ([[https://wiki.debian.org/DHCP_Serve | Ref]])