ubuntu 13.04 - dhcp and nat server

configure your public and private network interface(use 2 nic):
edit /etc/network/interfaces:
	sudo nano /etc/network/interfaces

	# public network interface
	auto eth0
	iface eth0 inet dhcp

	# private network interface
	auto eth1
	iface eth1 inet static
	address 192.168.182.1
	netmask 255.255.255.0
	broadcast 192.168.182.255
	network 192.168.182.0

install and configure DHCP service:
install isc-dhcp-server:
	sudo apt-get install isc-dhcp-server

specify that the private network interface is the one using the dhcp service:
edit /etc/default/isc-dhcp-server:
	sudo nano  /etc/default/isc-dhcp-server

	change the interface:
	INTERFACES="eth1"

configure the dhcp:
edit /etc/dhcp/dhcpd.conf:
	sudo nano /etc/dhcp/dhcpd.conf

	default-lease-time 600;
	max-lease-time 7200;

	option subnet-mask 255.255.255.0;
	option broadcast-address 192.168.182.255;
	option routers 192.168.182.254;
	option domain-name-servers 8.8.8.8, 8.8.4.4;
	option domain-name "yourdomainname.com";

	subnet 192.168.182.0 netmask 255.255.255.0 {
	range 192.168.182.100 192.168.182.199;
	}


CONFIGURE NAT:

enable ufw(uncomplicated firewall):

	by default deny everything:
		sudo ufw default deny

	allow SSH:
		sudo ufw allow ssh

	turn on firewall logging:
		sudo ufw logging on

	enable ufw(firewall):
		sudo ufw enable


enable ip forwarding:
edit /etc/sysctl.conf:
	sudo nano /etc/sysctl.conf

	uncomment:
		net.ipv4.ip_forward=1

configure iptables to allow internet connection sharing:
edit /etc/rc.local:
	sudo nano /etc/rc.local

	add the following below before the exit 0:
		/sbin/iptables -P FORWARD ACCEPT
		/sbin/iptables --table nat -A POSTROUTING -o eth0 -j MASQUERADE


restart ubuntu server:
	sudo reboot