In this topic I will provide basic information about Network addressing space. the global and other specialized IPv4 address blocks that have been assigned by the Internet Assigned Numbers  Authority (IANA).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, The value in each octet ranges from 0 to 255 decimal, or 00000000 – 11111111 binary.

Network Masks

IP address can be determined by three left most bits in the first octet and network mask helps you to identify the node.

Default masks are shown here :

Class A:

Class B:

Class C:

To understand how mask helps to identify the network and node in addresses convert them into binary numbers. = 00000100.00010000.00001111.00000001 = 11111111.00000000.00000000.00000000

netid =  00000100 = 4

hostid = 00010100.00001111.00000001 = 16.15.1

Any address bits which have corresponding mask bits set to 1 represent the network ID and 0 represents the node ID.

Different Classes defined by Internet Assigned Numbers  Authority (IANA).

CLASS A (1-127)               Private-Use Networks              Public-Data Networks              Cable Television Networks               Reserved but subject to allocation

127 network ID is excluded from this address class              Loopback

CLASS B  (128-191)             Reserved but subject to allocation        Link Local ,Hosts obtain these  addresses by auto-configuration,such as when a DHCP server may not  be found.           Private-Use Networks         Reserved but subject to allocation             Reserved but subject to allocation

  CLASS C (192- 223 )                        “Test-Net “ It is often used in conjunction with domain names in vendor and protocol documentation.Addresses within this block should not appear on public internet.          6to4 Relay Anycast  address.          Private-Use Networks             Network Interconnect Device Benchmark Testing       Reserved but subject to allocation

  CLASS D (224)                                Multicast

  CLASS E (240)                   Reserved for Future Use

Below table provide details about number of network,address per network and total addresses in class.

IP address-subnets