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 192.168.3.2. 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 255.255.255.0, 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
255.0.0.0	192.168.10.100	192	168.10.100
255.255.0.0	192.168.10.100	192.168	10.100
255.255.255.0	192.168.10.100	192.168.10	100

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