Introduction to IP Addressing

This document gives you basic information needed in order to configure your router for routing IP, such as how addresses are broken down and how sub netting works. 

The main requirement for IP Addressing is to have a sound knowledge of binary and decimal numbers.

Definition of some main words used in the process.

·         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.

Understanding IP Addresses

An IP address is an address used in order 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.

Here is how binary octets convert to decimal: The right most bit, or least significant bit, of an octet holds a value of 2⁰. The bit just to the left of that holds a value of 2¹. This continues until the left-most bit, or most significant bit, which holds a value of 2⁷. So if all binary bits are a one, the decimal equivalent would be 255 as shown here:

  1  1  1  1 1 1 1 1

128 64 32 16 8 4 2 1 (128+64+32+16+8+4+2+1=255)

 this is sample shows an IP address represented in both binary and decimal.

        10.       1.      23.      19 (decimal)

  00001010.00000001.00010111.00010011 (binary)