Basics of IP Addresses

In IPv4 the address is 32 bit (4 bytes) long. We represent the address using dotted decimal notation. i.e. decimal numbers 0-255 (represent a byte), is called octet, and each of that octets separated by '.',

for e.g. 192.168.1.1 the hex equivalent (hexadecimal) of this address is C0.A8.1.1 and binary (1100 0000. 1010 1000. 0000 0001 . 0000 0001) i.e. the equivalent integer is 3232235777 in decimal and C0A80101 in hex.

IP Classification

• IP addresses are classified into 5 categories
• Helps in orderly arrangement and efficient application of addresses along different networks
• classes can be A, B, C, D, E

Class Name	Starting bits of of MSO (Most significant bits of Most significant Octet i.e.Left most octet)	Range of Left Most Octet
A	0	0-127
B	10	128-191
C	110	192-223
D	1110	224-239
E	1111	240-255

Number of octets to represent net id and host id in different ip classes:- netid always start from left most octet. Based on the bits the default subnet mask can be determined so that to identify the netid and hostid.

IP Address divided into Net and Host Portions

Class A ip address (Address start with a number between 0 to 127 )

Class B IP Address (Address start with a number between 128 to 191 )

Class C IP Address ( Address start with a number between 192 to 223)

Class Name -(net id/host id )

A -(1/3)

B -(2/2)

C -(3/1)

thus the default subnet masks can be determined by checking the starting bits and the corresponding host and net id division above, thus the default subnet masks for each class is,

A - 255.0.0.0

B - 255.255.0.0

C - 255.255.255.0

This kind of addressing is classful addressing, but it result in wasting/insufficient number of ip addresses in different classes so there is another kind of routing that use classless routing and is known as CIDR (Classless Inter Domain Routing), it uses an ip with CIDR value denoted by preceding / (e.g. 192.168.1.1 /16) instead of the default subnet mask for classful address. Thus the classless addressing can use variable length blocks of ip addresses and thus solving the issue of address wasting or insufficient address in a particular class.

Reserved IP addresses

127.0.0.0 - Default Routing

255.255.255.255 - Global broadcast address

Private IP address ranges for different classes

class A - 10.0.0.0 to 10.255.255.255

class B - 172.16.0.0 to 172.31.255.255

class C - 192.168.0.0 to 192.168.255.255

Types of addresses

Unicast - one to one

Multicast - One to many

Broadcast - One to All

Not:e:-

IPv6 address is 128bit i.e. 16 byte long.