IP ADDRESSING

Introduction
This document will give you basic information you will need to configure your router for routing IP, such as how addresses are broken down and how subnetting works. You will learn how to assign each interface on the router an IP address with a unique subnet. And do not worry, we will show you lots of examples to help tie everything together.
Prerequisites
Requirements
There are no specific prerequisites for this document.
Components Used
This document is not restricted to specific software and hardware versions.
Additional Information
If definitions are helpful to you, use these vocabulary terms to get you started:
· Address—The unique number ID assigned to one host or interface in a network.
· Subnet—A portion of a network sharing a particular subnet address.
· Subnet mask—A 32-bit combination used to describe which portion of an address refers to the subnet and which part refers to the host.
· Interface—A network connection.
If you have already received your legitimate address(es) from the InterNIC (Internet Network Information Center), you are ready to begin. If you are not planning on connecting to the Internet, we strongly suggest that you use reserved addresses from RFC 1918 .
Conventions
For more information on document conventions, see the Cisco Technical Tips Conventions.
Understanding IP Addresses
An IP address is an address used to uniquely identify a device on an IP network. The address is made up of 32 binary bits which can be divisible into a network portion and host portion with the help of a subnet mask. The 32 binary bits are broken into four octets (1 octet = 8 bits). Each octet is converted to decimal and separated by a period (dot). For this reason, an IP address is said to be expressed in dotted decimal format (for example, 172.16.81.100). The value in each octet ranges from 0 to 255 decimal, or 00000000 - 11111111 binary.