3Com 3C840 IP Addressing, Introduction to IP, Administrators that are new to the IP protocol

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IP ADDRESSING

Introduction to IP	This section contains a brief introduction to the IP addressing scheme for
Addressing	administrators that are new to the IP protocol.

IP Addressing Basics IP addresses are 32 bits long and generally written in what is called dotted decimal notation: four decimal values separated by periods. For example: 192.77.203.5.

Address Classes In IP, the same 32 bits can be divided in a number of different ways to indicate networks and sub-networks of different sizes. The IP Network is identified by the number of bits in the network mask. The node addresses are not physical addresses of your network interface cards, but arbitrary numbers that are mapped to those physical addresses later. This allows you to accommodate varying network structures from a small number of network segments with huge numbers of nodes to large numbers of networks with only a few nodes.

Subnetting A large IP network can be subdivided into smaller subnetworks. This is done using a subnet mask (in this text, often called netmask), which tells a routing device how to further subdivide the Host ID portion of an IP address.

A subnet mask is a 32-bit value which also can be written in dotted decimal notation. It contains a number of bits set to 1 (indicating the network portion of an address) followed by a number of bits set to 0 (indicating the host portion of an address).

For example, a netmask of 255.255.255.0 on a Class B network would indicate that the network is divided into 254 sub-networks of 254 nodes each (0 and 255 are reserved numbers). For example, 128.5.63.28 would