An IP address allows a device to have a unique logical address to locate the device on the TCP/IP network and group it with others for network design and management purposes.

The remaining addresses known as Class E are reserved for experimental use.

An address comprises 2 parts:

The IP address comprises four sets of decimal numbers called octets, each separated by a period, with a value from 0 to 255 that represents a converted binary-to-decimal number

Classless addressing (also known as CIDR or supernetting) was developed to improve current Internet problems regarding the efficient utilization of address space. It also is used to add to the routing scalability of networks. Allocating portions of the large but limited number of addresses to an enterprise all at one time often resulted in the waste of some reserved addresses. Including each network in a table resulted in overload. Also, medium-sized enterprises that fit the class B category have multiplied the fastest, using much of the space in that class. Classless addressing, by allowing the delineation point between network information and host information to be flexible, has expanded the number of addresses available to all sizes of enterprise and has reduced the size of routing tables.

Public addresses, for use on the Internet, are assigned by a governing organization called the Internet Assigned Numbers Authority (IANA). However, your company may already have been assigned a section of addresses and your IT person can allocate the quantity that you need. If you have not been given a predefined set of IP ranges, you should be aware that the following three blocks have been reserved by IANA for private Internets:

10.0.0.0 - 10.255.255.255 (10/8 prefix)

172.16.0.0 - 172.31.255.255 (172.16/12 prefix)

192.168.0.0 - 192.168.255.255 (192.168/16 prefix)

There are three types of special addresses that should be mentioned:

A broadcast message, usually used for network management and diagnostic purposes, is addressed to all stations on the network. The destination address in a broadcast message is made up of all 1s (255.255.255.255).

A loopback address is used to test the implementation of the TCP/IP protocol on a host. The lower layers are bypassed by sending to a loopback address. This allows the higher layers (IP and above) to be tested without exposing problems at the lower layers. 127.0.0.1 is the address typically used for loopback testing.

As described in the previous section, network address refers to the network portion of an IP (Internet Protocol) address.

In planning for your network, you should anticipate the need for these addresses:

Tools can be found on the Internet to help calculate the number of addresses your network requires.

Forming subnets divides a large network into more manageable segments; it can allow you to expand the number of networks, while using only the single IP address. You need not apply for more of the limited number of IP address numbers.

Network traffic is reduced by sending messages to only a limited segment of the network. Subnetting can be particularly helpful on a network that handles a lot of broadcast traffic. It can also be useful if you have a slow WAN link connecting your far-flung locations.

To subnet, the default subnetwork mask for a network is extended to cover bits of the address that would otherwise be part of the host field. Once these bits are masked, they become part of the network field and are used to identify subnets of the larger network.

For a subnet with 64 addresses, the subnetwork mask is 255.255.255.192. The IP address would therefore be 192.168.1.1, the network address would be 192.168.0 and the host range would be from 0.1 to .63.

By using subnets in your plant, you can divide the plant into sections to avoid traffic overload. Use a router to pass traffic between subnets. There should be no more than 200 to 300 devices per network. However, it is preferable to have a smaller network with 50 to 100 devices. Add networks if you must accommodate more devices than the preferred number.

You may obtain addresses from the governing organization or use a group of those already assigned to your company. The next step is to assign a unique address to each end device by one of several methods. In static addressing, each user is assigned one fixed IP address to be used every time the user connects to the Internet. Dynamic addressing assigns the IP automatically, as needed. BootP (Bootstrap Protocol) as its name suggests, allows a workstation to configure itself without a hard drive or floppy disk. The workstation can discover its own IP address, the IP of a server and a file to be loaded into memory to boot the machine. DHCP assigns a different address to a device when it requests one. The software, rather than the administrator as in static addressing, keeps track of the IP addresses.