Lesson-6 Sub Netting Mechanics.

Hello friends today i going to share a most important lesson " SUB NETTING MECHANISM " . So please try to learn about this with carefully.

Subnetting Basics.

•          Subnetting provides

–--Addressing flexibility

----smaller Broadcast domains

---Easier to manage & provide security

•                 

To create subnets, some host bits are reassigned, or borrowed as network bits.

To determine the number of bits to borrow:

– Calculate how many hosts the largest subnet requires

– Calculate the number of subnets needed

Sub netting Basics(contd.)

•          Borrowing Bits to Grow a Subnet

•          The key concept in sub netting is borrowing bits from the host portion of the network to create a sub network.

•          Rules govern this borrowing, ensuring that some bits are left for a Host ID.

•          The rules require that two bits remain available to use for the Host ID& that all of the subnet bits cannot be all 1s or 0s at the same time.

•          For each IP address class, only a certain number of bits can be borrowed from the host portion for use in the subnet mask.

What we need!

•          Understand Address System

•          Understand Classes of Networks

•          “Two-Tums” Table

–      Formulas

–      Magic Numbers

–      Subnet Mask

•          “ANDing” Process

To Understand Address System

Understand Classes of Networks

 

Mask

 

 

 

 

 

TWO-TUMS

MAGIC NUMBERS:

128   64    32    16    8     4      2     1

2⁷      2⁶       2⁵       2⁴       2³      2²        2¹      2⁰

128 192 224 240 248 252 254 255

Subnet Mask.

•          The function of a subnet mask is to determine whether an IP address exists on the local network or whether it must be routed outside the local network

•          If the extracted network address matches the local network ID, the destination is located on the local network.

•          However, if they don’t match, the message must be routed outside the local network.

•          It is applied to a message’s destination address to extract the network address

•          The process used to apply the subnet mask involves Boolean Algebra to filter out non matching bits to identify the network address. ANDing Determines the Network(Subnet IP)

 
Subnet Mask(contd.)
 

 Subnet Mask(contd.)

•          If Four bits were borrowed, the mask for a Class C address would be 255.255.255.240

•          or 255.255.255.240/28

•          The fourth octet, 240 = 111100000

•          CIDR(Classless Inter Domain Routing)  

•          The /28 = the total network and subnet bits

•          – For a Class C this means 4 bits are borrowed;

•          8+8+8+4

•          – For a Class B this means 12 bits are borrowed;

•          8+8+8+4

•          – For a Class A this means 20 bits are borrowed;

•          8+8+8+4

Subnetting Terminology

•          **The binary value of the last bit borrowed is the range.

•          The first and last range of addresses are not usable.

•          The first address in each subnet range is the subnet number.

•          The last address in each subnet range is the subnet broadcast address.

 

Assessment

•          An IP Address 135.27.72.45

•          Subnet the Network with minimum 45 hosts per subnet.

1.Class:B

We can Identify the class easily  to see  the leading bit range of this IP Address.

2.Default subnet Mask:255.255.0.0

3.No. of  Hosts/Subnet:62

2n – 2  [Here n=6 bits borrowed for host portion]

Assessment (contd.)

4.No. of Usable Subnets:

2n=1024(n=10 bits)

5.Subnetwork Mask:255.255.255.192

8 bit=128 +64+32+16 +8+ 4+2+1

2 bit=128+64

##6 bits Borrowed from the host portion. So Sub network portion Left 10 bits.

Assessment (contd.)

6.Subnet IP:135.27.72.0

                                      10000111.00011011.01001000.00101101

                                      11111111.11111111.11111111. 11000000

                ANDing        10000111.00011011.01001000 .00000000

7.CIDR notation of given IP: 135.27.72.45 /26

Total network and subnetwork bits=8+8+8+2

8.Broadcast Address of the derived subnet: 135.27.72.63

The Broadcast Address is created by using binary Ones(1’s)  in the host bits, and Zeros(0’s) in the network and subnet bits.

Here Subnet IP:135.27.72.0

            01001000.00 0 0 0 0 0 0

            00000000.00 1 1 1 1  1 1

“Xor”   01001000.00 1  1 1 1 1 1

                               32+16+8+4+2+1=63

Assessment (contd.)

9.Given IP exists in Subnet No:288

 We have 10 bits in the subnet of given IP. So add all of the place valued bits .

      01001000.00 101101

     256+32=288

10.Two Usable hosts of the derived Subnet:

 135.27.72.1 , ,135.27.72.2

11. Host Range: 135.27.72.1---------135.27.72.62