Ethernet addresses are guaranteed to be unique but cannot be used because TCP/IP can run over many different physical media.

The unique addressing in a TCP/IP network is carried out at the network layer. Since it is the IP protocol which sits at the network layer the addressing scheme is commonly called IP addressing. The IP address hides the physical network details.

Basic format

IP addresses can be broken into two main parts

• The Network ID
• The Host ID

This separation allows routers to know whether a destination is local or needs to be routed.

Golden rules are for any two machines to communicate with each other:

• The addresses are unique
• The machines have the same Network ID unless there is a router between them.

Every host will have at least one IP Address maybe more. There will actually be one IP address for every network card. If a machine has three network cards then it will have three separate IP addresses.

Registering IP addresses

Although the IP addressing scheme allows unique addresses there is only one way to guarantee that a given address is unique.

To get a unique address you must register with NIC.

  Government Systems Inc.
  Attn: Network Information Centre
  14200 Park Meadow Drive
  Suite 200
  Chantilly, VA 22021
  Help Desk number: 1-800-365-3642

Officially you need only register your addresses with NIC if you wish to connect to the Internet. It may be worthwhile registering in any case so that you can rest assured that your IP addresses are unique and that you can easily connect to TCP/IP machines that are outside your control. Please note, however if you are absolutely sure that you will never have to connect to machines outside your internet then you can just pick numbers out of the air.

The only problems will arise when you need to connect to other machines that have by chance chosen the same IP addresses as yourself. Most people do not deal with NIC directly. Most sites will have a central network team that are responsible for assigning IP addresses within your organisation.

Normally a whole network id is assigned and you are at liberty to use any valid addresses within that network ID. If you run out of addresses in the range given then you will need to apply for another network id. One problem is that IP addresses are running out. This is an issue which must be addressed in the next year or two.

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