Sunday, 7 February 2021

Subnet Mask

What is Subnet Mask?

subnet mask is a 32-bit number created by setting host bits to all 0's and setting network bits to all 1's. Subnet Mask is used to drive the net ID. It also defines the class of IP-Address. The “255” address is always assigned to a broadcast address, and the “0” address is always assigned to a network address. 

            CLASS  SUBNET MASK

            A            255.0.0.0

            B            255.255.0.0

            C            255.255.255.0

Subnetting IP-Address

e.g. Class C = 192.168.10. 5

                         N               H

CIDR - CLASSLESS INTER DOMINE ROUTING

Subnetting

            It is to divide a large N/W into smaller N/W. It is the borrowing of bits from Host partition.

By Sub-netting one IP-Address wastage of IP –Address is avoided, it is achieved by CIDR (or) Slash Notation.

1- ON BIT

0- OFF-BIT

CIDR –VALUE ( CLASSLESS INTERDOMINE ROUTING )

Borrowing bit for Classes:

                                          N

CLASS A – 9 to 32  = 11111111.   00000000.   00000000.  00000000

                                  1            8    9         16     17        24   25         32         

                                          N                   N

CLASS B – 17 to 32 = 11111111.  11111111.   00000000.  00000000

CLASS C – 25 to 32 = 11111111.   11111111.  11111111.   00000000 

CIDR VALUE

2nd  OCTET             3rd                       4th

CLASS A            CLASS B         CLASS C

9                              17                    25

10                            18                    26

11                            19                    27

12                            20                    28

13                            21                    29

14                            22                    30

15                            23                    31

16                            24                    32

PROBLEM:

IP-ADDRESS : 192.168.10.0 / 27

DEFAULT SUBNET MASK: 255.255.255.0

STEP 1

11111111.   11111111.  11111111.   11100000 

1            8    9         16     17        24   25         32       

128          256

 64          -224

 32             32 – SUBNET MASK

224

STEP 2

To find out the subnet ID =256 - Subnet value

                                         = 256 - 224

                                                 32

STEP 3                           

To find out the number of subnets = 2x

                                                      =23

                                                         8

x- no of ‘ON’ bits in the net portion & Host portion

 STEP 4

To find out the number of host possible in one subnet in one subnet = 2- 2

                                                                                                             =2 - 2  =  32 -2 = 30

 y- no of ‘ OFF ‘ bits in the Host portion

STEP 5

1]192.168.10.0 -1st subnet ID

   192.168.10.1 – 2nd IP- ADRESS

   192.168.10.2

   ……………..

   192.168.10.30 – Last IP- ADDRESS

2]   192.168.10.31 – BROAD CAST ADDRESS                                                                                                                

   192.168.10.32

   192.168.10.33

    ……………..

   192.168.10.62

   192.168.10.63

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Also Learn About Managing Disk

 

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