DHCP server and NAT setup

Ubuntu/Debian Setup to make device eth0 dhcp server, and translate internet connection from wlan0
always as ROOT!!!!!!

# vim /etc/default/dhcp3-server
and set
INTERFACES="eth0"

# vim /etc/network/interfaces
and add

auto eth0
iface eth0 inet static
    address   10.1.1.254
    netmask   255.255.255.0
    broadcast 10.1.1.255
    network   10.1.1.0

run
# /etc/init.d/networking restart

# vim /etc/dhcp3/dhcpd.conf
and set only

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

option domain-name-servers 208.67.222.222, 208.67.220.220;

subnet 10.1.1.0 netmask 255.255.255.0 {
  range 10.1.1.10 10.1.1.20;
  option routers 10.1.1.254;
  option broadcast-address 10.1.1.255;
}

run
# /etc/init.d/dhcp3-server restart

if e.g. wlan0 is connected to the net, to translate internet connection to any dhcp client connected to eth0 (directly or through a switch), must be executed this script (modify accordingly)

-- script start --

#!/bin/bash

echo 1 > /proc/sys/net/ipv4/ip_forward

WAN="wlan0"
LAN="eth0"

/sbin/iptables -t nat -A POSTROUTING -o $WAN -j MASQUERADE
/sbin/iptables -A FORWARD -i $WAN -o $LAN -m state --state RELATED,ESTABLISHED -j ACCEPT
/sbin/iptables -A FORWARD -i $LAN -o $WAN -j ACCEPT

-- script end --

if things don't work following the steps, reboot client and server and rerun the script on server