TCP/IP Addressing

Anyone who has worked with TCP/IP knows that TCP/IP addressing can be a complex topic. This section provides an overview of TCP/IP addressing to compare how other protocols handle addressing.

In the most commonly deployed version of TCP/IP, version 4, (IPv4) addresses are composed of four sets of 8 bits referred to as octets. These are expressed in numbers and separated by periods. An example of a TCP/IP address is This format is often referred to as a 32-bit dotted decimal.

A single TCP/IP address represents both the IP address of an individual system and the network to which the system is attached. Determining which part of the IP address belongs to the network and which belongs to the node is the responsibility of the subnet mask. If part of the address refers to the network, it is assigned a binary value of 1 within the subnet mask. If it is the node address, it's assigned a binary value of 0 within the subnet mask.

For example, if you had a subnet mask of, the first two octets refer to the network and the second refer to the node address. So using the previous IP address as an example, the 192.168.3 portion of the address represents the network ID, and the .2 portion of the address represents the node ID. Table 5 shows default subnet masks and addressing examples.

Table 5 Determining Network and Node Addresses

Subnet Mask

IP Address

Network Address

Node Address







TCP/IP Interoperability

Of all the protocols used on today's networks, TCP/IP is by far the most versatile and interoperable. All of the popular operating systems today not only support TCP/IP, but the vast majority also use it as the default protocol. This means that in any network environment, you can have Linux, Windows, and NetWare servers and clients all communicating using TCP/IP.

TCP/IP Naming

Systems on a TCP/IP network can be accessed from the network either by their IP address or by a hostname. Hostnames are the names assigned to the system to make them easier to remember. For instance, the secretary's computer might have the address of, but you can access it using its hostname of secretary1 or whatever name you assign it.

The name-resolution process from IP address to hostname is often performed dynamically through a Domain Name Server (DNS). It can also be done statically using a text file called 'Hosts,' which is stored on each system.