IP ADDRESSING

An IP (internet protocol) address is a unique identifier for a node or host connection on a network. An IP address is a 32 bit (IPv4) binary number usually represented as 4 decimal values, each representing 8 bits, in the range 0 to 255(2 power 8 = 256 - known as octets) separated by decimal points. This is known as "dotted decimal" notation.

Example : 140.179.220.200

It is sometimes useful to view the values in their binary form

140 .179 .220 .200
10001100 .10110011 .1101100 .11001000

Every IP address consists of two parts, one identify the network and one identifying the node. Node can be any network resources such as server, client and printer. The Class of the address and the subnet mask determine which part belongs to the network address and which part belongs to the node address.

Address Classes

- There are 5 different address classes. You can determine which class any IP address is in by examining the first 4 bits of the IP address.

No Class type IP range
1 Class A address Begin with 0xxx or 1 or 126 decimal
2 Class B address Begin with 10xx or 128 or 191 decimal
3 Class C address Begin with 110x or 192 or 223 decimal
4 Class D address Begin with 1110 or 224 or 239 decimal
5 Class E address Begin with 1111 or 240 or 254 decimal

- Address beginning with 01111111, or 127 decimal , are reserved for loopback and for internal testing on a local mahcine. You can test this and should be able to ping 127.0.0.1, which points to your own computer.

- Class D addresses are reserved for multicasting . Multicasting application example is video conferensing using H.323 and H. 320 protocols. Class E addresses are reseved for future use. They should not be used for host addressess.

-Now we can see how the Class determines, by default, which part of the IP address belongs to the network (N) and which part belongs to the node (n)

4 octets -- XXXXXXXX.XXXXXXXX.XXXXXXXX.XXXXXXXX
------------------------------------------------------------------------------------------
1. Class A --NNNNNNNN.nnnnnnnn.nnnnnnnn.nnnnnnnn
2. Class B --NNNNNNNN.NNNNNNNN.nnnnnnnn.nnnnnnnn
3. Class C --NNNNNNNN.NNNNNNNN.NNNNNNNN.nnnnnnnn

- In the example, 140.179.220.200 is a Class B address so by default the Network part of the address (also known as the Network Address) is defined by the first two octets (140.179.x.x) and the node part is defined by the last 2 octets (x.x.220.200).

- In order to specify the network address for a given IP address, the node section is set to all "0"s. In our example, 140.179.0.0 specifies the network address for 140.179.220.200. When the node section is set to all "1"s, it specifies a broadcast that is sent to all hosts on the network. 140.179.255.255 specifies the examples broadcast address. Note that this is true regardless of the length of the node section.

- The summary :

Network portion Host portion Description
140.179 220.200 Class B address
140.179 0.0 Network address – all 0’s
140.179 255.255 Broadcast – all 1’s
255.255 0.0 Default class B subnet mask