www.advancedco.com
9
2.1.1 IP Address
An IP Address is a unique address which allows a device to be identified on a computer network.
IP Addresses essentially come in two forms:
Public / Static IP Address
Private IP Address
A public (or static) IP address allows a device to exist on the internet. Many Internet Service Providers (ISP)
offer packages which include static IP addresses as part of a package.
A private IP address is an address which exists on a private network, i.e. home network or business LAN. An
address is considered private if it falls within one of the following ranges:
10.0.0.0 through 10.255.255.255
169.254.0.0 through 169.254.255.255 (Automatic Private IP Addressing (
only)
172.16.0.0 through 172.31.255.255
192.168.0.0 through 192.168.255.255
Devices with private IP addresses cannot be accessed directly from the internet. Instead these devices are
accessed through a router via a Network Address Translation (NAT).
2.1.1.1 Network Address Translation (NAT)
A Network Address Translation is applied to a Router to allow a device on a private network to be accessed
from the internet. Consider the following network setup:
Private LAN
Router with External IP Address
212.188.225.200
10.101.100.21
10.101.100.25
10.101.100.30
Web Server
PC
ipGateway
www
External Port
Internal Port
Internal IP Address
10.101.100.25
10.101.100.21
10.101.100.30
80
8000
9010
80
8000
80
Router NATs
Public Network
(Internet)
Private Network
(LAN)
The NATs are shown in the table below the router.
The three internal devices (Web Server, PC, ipGateway) can now be accessed from the internet. The following
three examples describe how an external user can access these three devices.
