########### bridge_virtualbox.sh ##############

#!/bin/sh

# create a tap1 (network interface for Virtual Box)
tunctl -t tap1 -u <host user>
ip link set up dev tap1

# create the bridge
brctl addbr br0
brctl addif br0 tap1

# set the IP address and routing
ip link set up dev br0
ip addr add 10.1.1.1/24 dev br0
ip route add 10.1.1.0/24 dev br0

###### NAT Rules ######

# set the internal interface
INTIF="br0"

# set the external interface
EXTIF="<Network interface. Ex: eth0>"

# enable routing on Linux
echo 1 > /proc/sys/net/ipv4/ip_forward

# clear existing iptable rules, set a default policy
iptables -P INPUT ACCEPT
iptables -F INPUT
iptables -P OUTPUT ACCEPT
iptables -F OUTPUT
iptables -P FORWARD DROP
iptables -F FORWARD
iptables -t nat -F

# set forwarding and nat rules
iptables -A FORWARD -i $EXTIF -o $INTIF -j ACCEPT
iptables -A FORWARD -i $INTIF -o $EXTIF -j ACCEPT
iptables -t nat -A POSTROUTING -o $EXTIF -j MASQUERADE

########### bridge_virtualbox.sh ##############

# sudo apt-get install dhcp3-server

INTERFACES="br0"

ddns-update-style interim;
ignore client-updates;

subnet 10.1.1.0 netmask 255.255.255.0 {

	option routers			10.1.1.1;
	option subnet-mask		255.255.255.0;

	option domain-name-servers	<DNS server ip address. Look at ip in /etc/resolv.conf>;

	range dynamic-bootp 10.1.1.2 10.1.1.254;
	default-lease-time 21600;
	max-lease-time 43200;
}

# sudo sh /bridge_virtualbox.sh
# sudo /etc/init.d/dhcp3-server start