IPv4 Addressing

Addressing of IPv4


                                     In the previous chapter, we looked at the network layer and its involvement in communication. in this chapter, we will look at ipv4 addressing. This is one of the most important concepts in networking and will be critical in your overall success in networking. Understanding this chapter is critical to the rest of your studies.

                                    Internet Protocol version 4 (IPv4) is the fourth version in the development of the Internet Protocol (IP) and the first version of the protocol to be widely deployed. IPv4 is described in IETF publication RFC 791 (September 1981), replacing an earlier definition (RFC 760, January 1980).

IP – Internet Protocol

  • IP has two types
                                                                1. Internet Protocol Version –  4
2. Internet Protocol Version  – 6

It is a Connection less Protocol

IP Address : Numbers are Seprated By Dot


IP Address : 192.168.100. 101

Every IPv4 is consist of Four Octet

octet means group of eight bit


Every IP has Two Information field

  1.  Network Field

  2.  Host Field

IP Address has 5 classes :

  • Class A  =  1     – 126
  • Class B  =  128 – 191
  • Class C  =  192 – 223
  • Class D  =  224 – 239
  • Class E  =  240 – 255

Class Of IP Address decided by First Octet

CCNA would be only deciding with Class A,B,C

Class D is used for Multi-cast

Class E is Reserved For Experimental  Purpose

More Than 255 decimal number is Invalid Ip

Addressing Classes – IPv4

The first octet referred here is the left most of all. The octets numbered as follows depicting dotted decimal notation of IP Address:


The number of networks and the number of hosts per class can be derived by this Formula:


When calculating hosts’ IP addresses, 2 IP addresses are decreased because they cannot be assigned to hosts, i.e. the first IP of a network is network number and the last IP is reserved for Broadcast IP.

Class A Addressig

1 –  Network field 

3 – Host Field

Ex :                                    ( 1- 126 = class A)

The first bit of the first octet is always set to 0 (zero). Thus the first octet ranges from 1 – 127, i.e.

Class A Addresses

Class A addresses only include IP starting from 1.x.x.x to 126.x.x.x only. The IP range 127.x.x.x is reserved for loopback IP addresses.

The default subnet mask for Class A IP address is which implies that Class A addressing can have 126 networks (27-2) and 16777214 hosts (224-2).

Class A IP address format is thus:   0NNNNNNN.HHHHHHHH.HHHHHHHH.HHHHHHHH

Class B Addressing

2 – Network Field

2 – Host Field

Ex : 172.123.100 225                                  ( 128 – 191 = Class B)

An IP address which belongs to class B has the first two bits in the first octet set to 10, i.e.

Class B Addresses

Class B IP Addresses range from 128.0.x.x to 191.255.x.x. The default subnet mask for Class B is 255.255.x.x.

Class B has 16384 (214) Network addresses and 65534 (216-2) Host addresses.


Class C Addressing

3 – Network field

1 – Host Field

Ex :                                            (192 – 223 = Class A)

The first octet of Class C IP address has its first 3 bits set to 110, that is:

Class C Addresses

Class C IP addresses range from 192.0.0.x to 223.255.255.x. The default subnet mask for Class C is 255.255.255.x.

Class C gives 2097152 (221) Network addresses and 254 (28-2) Host addresses.


Class D Address

Very first four bits of the first octet in Class D IP addresses are set to 1110, giving a range of:

Class D Addresses

Class D has IP address rage from to Class D is reserved for Multicasting. In multicasting data is not destined for a particular host, that is why there is no need to extract host address from the IP address, and Class D does not have any subnet mask.

Class E Address

This IP Class is reserved for experimental purposes only for R&D or Study. IP addresses in this class ranges from to Like Class D, this class too is not equipped with any subnet mask.

Posted By RamCruiseWalker




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