# Binary Lesson 6.1 Classful Subnetting 2

Networking and Communications

Oct 24, 2013 (4 years and 6 months ago)

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Binary Lesson 6.1

Classful

Subnetting

2

Slash Notation

Consider a class A address of 1.2.3.4

The network portion is the first octet

1

This situation can be written

1.2.3.4/8

The number after the / is the number of
bits in the network portion

Consider a class A address of 1.2.3.4 /8 in
binary

The

is 255.0.0.0

In Binary:

IP:

00000001 00000010 00000011 00000100

Subnt Msk:

11111111 00000000 00000000 00000000

00000001 00000000 00000000 00000000

AND

To find the network address, take a node's

If the Subnet mask bit is 1, keep the IP address bit

If the Subnet mask bit is 0, that bit changes to 0

This is called a bitwise AND operation

IP:

00000001 00000010 00000011 00000100

Subnt Msk:

11111111 00000000 00000000 00000000

00000001 00000000 00000000 00000000

Class B

The

is 255.255.0.0

In Binary:

IP:

10010011 10010000 00000001 11010100

Subnt Msk:

11111111 11111111 00000000 00000000

10010011 10010000 00000000 00000000

Class C

The

is 255.255.255.0

In Binary:

IP:

11000000 10101000 00000001 00001010

Subnt Msk:

11111111 11111111 11111111 00000000

11000000 10101000 00000001 00000000

192.168.1.0 /25

You can split a class C in half with a /25

IP:

192.168.1.10 /25

255.255.255.128

Network:

192.168.1.0

IP:

11000000 10101000 00000001 00001010

Subnt Msk:

11111111 11111111 11111111 10000000

11000000 10101000 00000001 00000000

192.168.1.0 /25

There are only 128 addresses in a /25 block

Network:

192.168.1.0 /25

1
st

Usable:

192.168.1.1

Last Usable:

192.168.1.126

192.168.1.127

Net Addr: 11000000 10101000 00000001 00000000

First Use: 11000000 10101000 00000001 00000001

Last Use:

11000000 10101000 00000001 01111110

11000000 10101000 00000001 01111111

192.168.1.128 /25

There are only 128 addresses in a /25 block

Network:

192.168.1.128 /25

1
st

Usable:

192.168.1.129

Last Usable:

192.168.1.254

192.168.1.255

Net Addr: 11000000 10101000 00000001 10000000

First Use: 11000000 10101000 00000001 10000001

Last Use:

11000000 10101000 00000001 11111110

11000000 10101000 00000001 11111111

192.168.1.0 /26

There are only 64 addresses in a /26 block

Network:

192.168.1.0 /26

1
st

Usable:

192.168.1.1

Last Usable:

192.168.1.62

192.168.1.63

Net Addr: 11000000 10101000 00000001 00000000

First Use: 11000000 10101000 00000001 00000001

Last Use:

11000000 10101000 00000001 00111110

11000000 10101000 00000001 00111111

192.168.1.64 /26

There are only 64 addresses in a /26 block

Network:

192.168.1.64 /26

1
st

Usable:

192.168.1.65

Last Usable:

192.168.1.126

192.168.1.127

Net Addr: 11000000 10101000 00000001 01000000

First Use: 11000000 10101000 00000001 01000001

Last Use:

11000000 10101000 00000001 01111110

11000000 10101000 00000001 01111111

192.168.1.128 /26

There are only 64 addresses in a /26 block

Network:

192.168.1.128 /26

1
st

Usable:

192.168.1.129

Last Usable:

192.168.1.190

192.168.1.191

Net Addr: 11000000 10101000 00000001 10000000

First Use: 11000000 10101000 00000001 10000001

Last Use:

11000000 10101000 00000001 10111110

11000000 10101000 00000001 10111111

192.168.1.192 /26

There are only 64 addresses in a /26 block

Network:

192.168.1.192 /26

1
st

Usable:

192.168.1.193

Last Usable:

192.168.1.254

192.168.1.255

Net Addr: 11000000 10101000 00000001 11000000

First Use: 11000000 10101000 00000001 11000001

Last Use:

11000000 10101000 00000001 11111110

11000000 10101000 00000001 11111111

Classful Subnetting
iClicker Questions

How many subnets containing 9
hosts each can be made from
this network?

192.168.1.0/24

A.
4

B.
8

C.
16

D.
32

E.
Something else

How many subnets containing 90
hosts each can be made from
this network?

192.168.1.0/24

A.
4

B.
8

C.
16

D.
32

E.
Something else

How many subnets containing 9
hosts each can be made from
this network?

147.144.1.128/26

A.
4

B.
8

C.
16

D.
32

E.
Something else

How many subnets containing 2
hosts each can be made from
this network?

192.168.1.0/27

A.
4

B.
8

C.
16

D.
32

E.
Something else

How many subnets containing
900 hosts each can be made
from this network?

10.0.0.0/16

A.
8

B.
16

C.
32

D.
64

E.
Something else

What subnet contains this host?

192.168.1.129/30

A.
192.168.1.126 /30

B.
192.168.1.128 /30

C.
192.168.1.126 /29

D.
192.168.1.130 /30

E.
Something else

What is the smallest subnet
containing these two hosts?

192.168.1.1

192.168.1.10

A.
192.168.1.0 /24

B.
192.168.1.0 /26

C.
192.168.1.0 /28

D.
192.168.1.0 /30

E.
Something else

What is the smallest subnet
containing these two hosts?

10.1.1.2

11.1.1.1

A.
10.0.0.0 /8

B.
10.0.0.0 /7

C.
10.0.0.0 /6

D.
8.0.0.0 /6

E.
Something else

What is the smallest subnet
containing these two hosts?

147.144.128.129

147.144.128.193

A.
147.144.128.0 /24

B.
147.144.128.0 /25

C.
147.144.128.128 /25

D.
147.144.128.128 /26

E.
Something else

What is the smallest subnet
containing these two hosts?

192.168.1.62

192.168.1.65

A.
192.168.1.0 /24

B.
192.168.1.32 /25

C.
192.168.1.0 /25

D.
192.168.1.32 /26

E.
Something else