1. Prepared by : Adeel Ahmad Updated by : Syed Ameen Quadri
Chapter 3: Easy Subnetting
Prepared by : Adeel Ahmad Updated by : Syed Ameen Quadri

2. One network
In the topic “TCP/IP,” we have learned how to define and find the valid host ranges used in a Class A, Class B, and Class C network address by turning the host bits all off and then all on. This is very good, but the problem is, you were defining only one network, as shown in below.

3. Multiple networks connected together
It is good to break up that one, huge network address and create four manageable networks from it? To make that happen, you would need to apply subnetting because it’s the best way to break up a big network it into a bunch of smaller ones. In the Figure below you can see how this will look.

4. Subnetting
The definition of Subnetting means, Dividing a Single Network into Multiple Networks.
Converting Host bits to Network Bits i.e. Converting 0’s into 1’s
Subnetting is of two type FLSM (Fixed Length Subnet Mask) and VLSM (Variable Length Subnet Mask)
When the number of subnet is fixed then it is FLSM, other wise it is a VLSM

5. To create a subnet, we’ll start by fulfilling these three steps:
Determine the number of required network IDs:
One for each LAN subnet
One for each wide area network connection
Determine the number of required host IDs per subnet:
One for each TCP/IP host. (PC, Printer, IP Phone etc.)
One for each router interface
Based on the above requirements, create the following:
A unique subnet mask for your entire network.
A unique subnet ID for each physical segment
A range of host IDs for each subnet

6. Table shows the default subnet masks for Classes A, B, and C.
Class Format Default Subnet
A network.node.node.node
B network.network.node.node
C network.network.network.node

7. Number of Networks and Hosts
Class A – Networks
Class B – 65, Networks
Class C – 2,097,152 Networks
Class A – 16,777,214 Hosts
Class B – 65, Hosts
Class C – Hosts

8. List of all subnet mask & its equivalent CIDR slash notation.
The /8 through /15 can only be used with Class A, network addresses.
/16 through /23 can be used by Class A and B network addresses.
/24 through /30 can be used by Class A, B, and C network addresses
Subnet Mask CIDR /8 /9
/10
/11
/12
/13
/14
/15
Subnet Mask CIDR
/16
/17
/18
/19
/20
/21
/22
/23
Subnet Mask CIDR
/24
/25
/26
/27
/28
/29
/30

9. Subnetting a Class C Address
When you’ve chosen a possible subnet mask for your network and need to determine the number of subnets, valid hosts and the broadcast addresses of a subnet that mask will provide, all you need to do is answer five simple questions:
How many subnets does the chosen subnet mask produce?
How many valid hosts per subnet are available?
What are the valid subnets?
What’s the broadcast address of each subnet?
What are the valid hosts in each subnet?

10. Subnetting Practice Examples: Class C Addresses
Since 128 is in binary, there is only 1 bit for subnetting and 7 bits for hosts. We’re going to subnet the Class C network address
= Network address
= Subnet mask

11. Steps of subnetting…
How many subnets? Since 128 is 1 bit on ( ), the answer would be 21 = 2.
How many hosts per subnet? We have 7 host bits off ( ), so the equation would be 27 – 2 = 126 hosts. Once you figure out the block size of a mask, the amount of hosts is always the block size minus 2. No need to do extra math if you don’t need to!

12. Steps of subnetting…
What are the valid subnets? 256 – 128 = 128. Remember, we’ll start at zero and count in our block size, so our subnets are 0, 128. By just counting your subnets when counting in your block size, you really don’t need to do steps 1 and 2. We can see we have two subnets, and in the step before this one, just remember that the amount of hosts is always the block size minus 2, and in this example, that give us 2 subnets, each with 126 hosts.

13. Steps of subnetting…
What’s the broadcast address for each subnet? The number right before the value of the next subnet is all host bits turned on and equals the broadcast address. For the zero subnet, the next subnet is 128, so the broadcast of the 0 subnet is 127.

14. Steps of subnetting…
What are the valid hosts? These are the numbers between the subnet and broadcast address. The easiest way to find the hosts is to write out the subnet address and the broadcast address, which makes valid hosts completely obvious.

15. Other example… Let us take an address as 192.168.1.0 /24
Here Default n/w bit =24 and host bit =8
Say required host is 50
Now we have to select the H value so that it should be greater than or equal to 50 form 2 to the power table.
So 2H = 26 = 64, this value is ≥ 50
That’s why H = 6
2^0
2^1
2^2
2^3
2^4
2^5
2^6 1 2 4 8 16 32 64

16. Example…
We got H = 6
Converted network bits = total hosts – required hosts
Converted network bits = 8 – 6 = 2
That is network bit N = 2
Total network bits = total + converted = = 26
Subnet = 2N = 22 = 4 that is total subnet is 4
Block size = 2H = 26 = 64

17. Example…
So from this data the range of IP Address is as follows. Subnet – Network IP – [Valid Host] Broadcast IP

18. Example…
So from this data the range of IP Address is as follows. Subnet – Network IP – [Valid Host] Broadcast IP

19. Example…
So from this data the range of IP Address is as follows. Subnet – Network IP – [Valid Host] Broadcast IP

20. Example…
So from this data the range of IP Address is as follows. Subnet – Network IP – [Valid Host] Broadcast IP

21. Exam 1 Chapter 1 and chapter 2 It’s of 15 Marks.
Monday, 20th March 2017
From 2pm – 3pm