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Every computer on a network has an IP Address (Internet Protocol Address) and each one must be unique so that other computers can find it. Think of it in the same way that every house in the UK has a unique postall address. Some houses share a Post Code, but none will have the exact same address, for example your neighbour will have the same Post Code as you, but their house number is different which makes their address unique. Two houses may have the same address (20 Credibilty Street) but they may be in different towns or have a different Post Code. Again, their addresses are unique.

Your server will be connected to the Internet so it needs a unique IP Address. How do you get that? Well, it depends on how you connect to the Internet, but for the average home user it is the same. You will have an ISP (Internet Service Provider) that you pay for allowing you access. They will provide you with a Router / Gateway / Livebox, whatever they want to call it, it is essentially the same thing, a NAT Router (Network Address Translation).

Think of this NAT Router as having two faces, one external side facing the Internet and one internal side facing your home network. These two sides will be referred to as the WAN port (Wide Area Network) and the LAN port (Local Area Network) sides. Bear in mind that these two ports are physical ports that you can see on your router.

There are two ways that the WAN port on your router will obtain an IP Address;
  • (a) Statically
  • (b) Dynamically
Statically: Your ISP will provide you with an IP Address that they own and this IP Address never changes. This system is used less and less these days and in fact you would almost certainly have to pay extra charges to be issued a static IP Address.

This scenario makes it very easy to find your server as it never moves.

Dynamically: Your ISP has bought a range of IP Addresses and will issue one to each of their customers, however, you are not guaranteed to get the same one each time you connect your Router to the Internet. If you disconnect your WAN port, the IP Address you were using will be relinquished and the ISP could issue it to a different customer when they connect their NAT Router.

This scenario makes it a little more tricky to find your router as it will move from time to time. It is not imposssible but will require further configuration.

The LAN side of your router also needs to be aware of IP Addresses, and usually your device will come configured for running DHCP (Dynamic Host Control Protocol) services, if not you will have to configure it. DHCP is just the name given to the service that gives each computer on your internal network a unique IP Address in much the same way that your ISP is issuing you with a dynamic IP Address. Your NAT router must issue unique addresses to each computer / device on your LAN. It is essential that you have this configured correctly or the NAT Router will not be able to function properly.

IP Addresses take the form of four 8 bit numbers and they are always accompanied by a subnet mask which is also four 8 bit numbers. The IP Address you use internally will be from what is known as a private range, that is they are not in use on the Internet and your router will never route information for them to the Internet so they are hidden They are only visible internally. That is why your home PC can have the same IP Address as your neighbour's home PC. They are invisible to each other as they are not on the same network. Only your NAT Router is on the same network as your neighbours, so your two WAN ports will have unique IP Addresses.

Private Ranges are usually either

We will use the latter example and a typical private IP Address will look like this
and the subnet mask that goes with this private range is

This means that every computer on your LAN will need the first 3 parts of the IP Address to be the same, i.e.


it is only the last octet which needs to be different, so a PC with an IP Address of

can communicate with a computer on and ip address of

if they both have the same subnet mask.

If you are running DHCP on your NAT Router's LAN ports, this will be taken care of, but if not you will need to allocate each of your copmputers an ip address and subnet mask accordingly. Just be aware that NAT Routers using different IP Ranges can have a different subnet mask such as

In this case, only the first 2 octets of your IP Addresses have to be the same, the last 2 can different and still communicate with eache other.

NOTE: To keep things simple, always use a subnet mask value of 255 or 0 and the value in an IP Address octet should only be between 2 and 254. You could use 1 but that will usually be taken by the router.

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