what is subnet ?

            Sub net is a logical subdivision of an IP network. it divided in to two types ;-  
1.network identifier or routing prefix
2.rest  field or host identifier

 

Host identifier is an identifier by which a specific host on network interface.

network identifier may be expressed in classless inter-domain routing (CIDR)

notation written as the first address of a network followed by a slash character () and ending with the bit-length of the prefix.

for example , 198.51.100.0/24 is the prefix of the internet protocol version 4 network starting at the given address.

24 bits allocated for the network prefix and 8 bits reserved for host address .

addresses in the range 198.51.100.06 to 198.51.100.255 belong to this network.

the IPV6 address specification 200; db 8;;32 is large address block with 296 addresses having a 32 bit routing prefix.

Reallocating IP address , Each class has a limited number of host allocations.

For example;-  If a network administrator is working with a class B or C network and needs to allocate 150 hosts for three physical networks located in three different cities,

they would need to either request more address blocks for each network  or divide a network into sub-nets that enable administrators to use one block of addresses administrators to use one block of addresses on multiple physical networks.

*Improving network security;-   Sub-netting allows network administrators to reduce network wide threats by quarantining compromised sections of the network and by making it  more difficult for trespassers  to it around an organisations network.

A sub-net mask is a number that defines a range of IP addresses available within a network .

Which particular network divided from a single network to smaller network that is called Sub-nets.

A Sub-net mask is used to divide an IP address into two parts.The Sub net mask is used by the TCP/IP

protocol to determine whether a host is on the local sub-net or  on a remote network.

It uses the same format as an IPv4 address – four sections of one to three numbers, separated by dots.

Each section of the sub-net can contain a number from 0-255, just like an IP address.

For example- A typical Sub-net mask for a class-C IP address is 255.255.255.0

If your computer is connected to a network, you can view the networks sub-net mask number in the  network control panel (windows) or Preference (Mac-OS).

Almost all decimal sub-net masks convert to binary numbers that are all ones on the left and all zeros on the right. some other common sub-net mask are;-

Basically Sub-net  mask divided into three type;-

* Class-A networks use a default sub-net mask of 225.0.0.0 and have 0-127 as their first octet.

The address 10.52.36.11 is a Class-A address. Its first octet is 10, which is between 1 and 126,

inclusive.

*Class-B networks use a default sub-net mask of  255.255.0.0 and have 128-191 as their first octet.

 The address 172.16.52.63 is a Class B address. Its first octet is 172, which is between 128 and 191,

inclusive.

*Class-C networks use a default sub-net mask of 255.255.255.0 and have 192-223 their first octet.

The address 192.168.123.132 is a class c address. Its first octet is 192 which is between 192-223,

inclusive.

*Class-D range -224-239

*Class-D range- 240-255

        These IP addresses have no Sub-

net mask .It is very special and very strong because It is reserved for development organization.

For example- NASA, ARMY AND Government sector.