Introduction to Networking
(Yarnfield)
Classful subnetting
Objective


To cover the subnetting process
Be able to subnet from a variety of information
Subnetting

The process of dividing a network up into subnets and to
assign each subnet a valid network IP address, and the
hosts on that subnet valid IP addresses
Subnet 2
Subnet 1
Subnet 3
We need to find out





How many subnets does the subnet mask provide?
How many valid hosts per subnet are available?
What are the valid subnets?
What is the broadcast address of each subnet?
What are the valid hosts in each subnet?
We need
An IP address to subnet
And
 The number of subnets we wish to make
Or
 The subnet mask
Or
 The number of borrowed bits

Example
192.5.5.35
255.255.255.224
Example
IP address: 192.5.5.35
 Subnet mask: 255.255.255.224
 Work out
1. Network ID Class
2. Major network address
3. Major broadcast address
4. First host of the major network
5. Last host of the major network

Class C
192.5.5.0
192.5.5.255
192.5.5.1
192.5.5.254
Example
IP address: 192.5.5.35
 Subnet mask: 255.255.255.224
 Now we need to work out the subnet information
3 subnet bits
1. Number of subnet bits
5 host bits
2. Number of host bits
3. Subnet address for the given host IP address

192.5.5.32
4.
Range of host addresses for this subnet
192.5.5.33 – 192.5.5.62
5.
Broadcast address for this subnet
192.5.5.63
Example
IP address: 192.5.5.35
 Subnet mask: 255.255.255.224
 Now we need to find other subnet information
1. Total number of useable subnets
2. Number of valid host IP addresses per subnet
3. Convert given subnet mask to binary

6
30
11111111.11111111.11111111.11100000
4.
Convert given host IP address to binary
11000000.00000101.00000101.00100011
5.
Subnetwork address with slash (/) mask for the assigned
subnet
192.5.5.32 / 27
Exercise

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
1.
2.
3.
4.
5.
6.
7.
8.
4.
5.
1.
2.
3.
4.
5.
IP address 202.168.2.40
Subnet mask 255.255.255.240
Find out:
Network ID Class
Major network address
Major broadcast address
First host of the major network
Last host of the major network
Number of subnet bits
Number of host bits
Subnet address for the given host IP address
Range of host addresses for this subnet
Broadcast address for this subnet
Total number of useable subnets
Number of valid host IP addresses per subnet
Convert given subnet mask to binary
Convert given host IP address to binary
Subnetwork address with slash (/) mask for the assigned subnet
Questions...

... are there any?