• IP Addressing is Logical Addressing
  
  
• It works on Network Layer (Layer 3)
  
  
• Two Version of Addressing Scheme

1. IP version 4 – 32 bit addressing
2. IP version 6 – 128 bit addressing

What is BIT ?

• Bit is a value that will represent 0’s or 1’s (i.e. Binary)

        01010101000001011011111100000001

• 32 bits are divided into 4 Octets known as Dotted Decimal Notation

• 128-bit address is divided along 16-bit boundaries, and each 16-bit block is converted to a 4-digit hexadecimal number and separated by colons (Colon-Hex Notation) 

                         FEDC:BA98:7654:3210:FEDC:BA98:7654:3210

                             This discussion is out of the scope of CCNA

Binary to Decimal Conversion

IP Address Classes

Priority Bits Concept

• To identify the range of each class 
   we will be using Priority Bit Concept
• Priority Bit is the left most bits in the First Octet
  

• CLASS A priority bit is                         0
• CLASS B priority bit is                         10
• CLASS C priority bit is                         110
• CLASS D priority bit is                         1110
• CLASS E priority bit is                         1111

CLASS A Range

For Class A range reserved first bit in 
first octet,the value of that bit should not change.

CLASS B Range

For Class B range reserved first two bit in 
first octet,the value of that bit should not change.

CLASS C Range

For Class C range reserved first three bit in 
first octet,the value of that bit should not change.

CLASS D Range

For Class D range reserved first four bit in 
first octet,the value of that bit should not change.



CLASS E Range
For Class E range reserved first four bit in 
first octet,the value of that bit should not change.

Octet Format

• IP address is divided into Network & Host Portion
• CLASS A is written as                              N.H.H.H
• CLASS B is written as                              N.N.H.H
• CLASS C is written as                              N.N.N.H

CLASS A – No. Networks & Host 

Class A Octet Format is N.H.H.H
Network bits : 8                     Host bits : 24

• No. of Networks 
   = 28-1 (-1 is Priority Bit for Class A)
   = 27
   = 128 – 2 (-2 is for 0 & 127 Network)
   = 126 Networks
• No. of Host  
   = 224 – 2 (-2 is for Network ID & Broadcast ID)
   = 16777216 - 2
   = 16777214 Hosts/Network

CLASS B – No. Networks & Host 

Class B Octet Format is N.N.H.H
Network bits : 16              Host bits : 16

• No. of Networks 
   = 216-2 (-2 is Priority Bit for Class B)
   = 214
   = 16384 Networks
• No. of Host  
   = 216 – 2 (-2 is for Network ID & Broadcast ID)
   = 65536 - 2
   = 65534 Hosts/Network

CLASS C – No. Networks & Host 

Class C Octet Format is N.N.N.H
Network bits : 24                 Host bits : 8

• No. of Networks 
   = 224-3 (-3 is Priority Bit for Class C)
   = 221
   = 2097152 Networks
• No. of Host  
   = 28 – 2 (-2 is for Network ID & Broadcast ID)
   = 256 - 2
   = 254 Hosts/Network
  
  
  

Network & Broadcast Address  

The network address is represented with all bits as ZERO in the host portion of the address

The broadcast address is represented with all bits as ONES in the host portion of the address

Valid IP Addresses lie between the Network Address and the Broadcast Address. 

Only Valid IP Addresses are assigned to hosts/clients

Example - Class A 

Example - Class B 

Example - Class C

Private IP Address

• There are certain addresses in each class of IP address that are reserved for LAN. These addresses are called private addresses.

• They can be used for: home & office networks, ATM machines, networks not connected to Internet.
  
  
  

Subnet Mask

• Subnet Mask differentiates Network portion and Host Portion
• Subnet Mask is been given for host Identification of Network ID
• Represent all Network Bit Values with 1
• Represent all Host Bit Values with 0

Subnet Mask - Examples 

How Subnet Mask Works ?

IP Address     : 192.168.1.1
Subnet Mask :  255.255.255.0

192.168.1.1       = 11000000.10101000.00000001.00000001
255.255.255.0 = 11111111.11111111.11111111.00000000
============================================
192.168.1.0      = 11000000.10101000.00000001.00000000
============================================

Above Calculations is done with the Help of AND Table. 
The output of an AND table is only 1 if both its inputs are 1. 
For all other possible inputs the output is 0.