# chapter 4

Networking and Communications

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

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Hands
-
On Microsoft
Windows Server 2003
Networking

Chapter Four

Subnetting

2

Objectives

Understand why subnetting is necessary

Describe how computers work with binary

Subnet any network

Determine the number of useable hosts on a
subnet

Supernet several smaller networks

3

Reasons to Subnet

Subnetting

The process of separating a network into several
smaller networks to improve performance

Subnetting is used because it can

Reduce collisions

Control traffic

4

Reducing Collisions

Collision

When two computers on an Ethernet network
using CSMA/CD as an access method attempt to
transmit at the same time

Subnetting

Reduces number of hosts on each network

Reduces the amount of traffic on the network

With less traffic, collision is reduced

Collisions that occur on one network do not
affect another network

5

Subnetting a network

Creates multiple networks with fewer hosts on
each network

Fewer hosts results in fewer broadcast messages

Routers

255.255.255.255 are not forwarded

6

Controlling Traffic

Routers

Allows a greater degree of control over network
traffic

Most have ability to implement rules about which
packets they forward

7

Binary and TCP/IP

Internally, computer looks at an IP address as a
single group of 32 binary digits

Decimal numbering

A base
-
ten numbering system

Uses the values from
0

to
9

for each digit

8

Counting in Decimal

9

Decimal Column Values

10

Binary Numbering

Subnetting

Based on binary

Binary

Base two numbering system

Two potential values for each digit:
0
and
1

11

Binary Counting

12

Binary Column Values

13

Conversion Between Binary and
Decimal

To convert a binary octet to a decimal value

Multiply the digit in each column by the value of
each column

Then determine the sum of those products

14

Binary to Decimal Conversion

15

Windows Calculator in Scientific
Mode

16

Computer calculates the host ID and network ID
of an IP address while working in binary

Part of the network ID

Where there is a
1

Part of the host ID

Where there is a
0

ANDing

Binary process used by computers to find the
network ID

the network ID

1s in a subnet mask must be contiguous

17

Calculating Host ID and Network ID

18

19

Subnetting a Network

To subnet a network

Take some bits from the host ID and give them to
the network ID

Normally very large

Generally need to be subnetted to handle routing
between different physical locations

Using an entire octet for subnetting gives 256
possible subnets

1
s and all
0
s are

20

Simple Subnetting

21

Complex Subnetting

22

Subnet Hosts

2
n
-
2
, where
n

is the number of host bits

Formula used to calculate the number of subnets
that can be created from a certain number of bits

Also used to calculate the number of usable hosts
on a subnet

23

Usable Hosts

24

Usable Hosts Formula

25

Supernetting

The opposite of subnetting

Used to create one large network from several
smaller ones

Takes bits from network ID and gives them to
the host ID

All networks being combined for supernetting
must be contiguous

IP addresses from first network to last must be
one single range with no breaks

26

Supernetting Two Class C Networks

27

Supernetting Four Class C Networks

28

Reasons for Supernetting

Supernetting

Used when a range of IP addresses larger than a
Class C network is required, but a full Class B
network is not required

May also be used to reduce routing complexity

29

Summary

Subnetting

Used to divide a single large network into multiple
smaller networks

Reduces packet collisions

Controls network traffic

Binary

Base
-
two numbering system

Only
0

and
1

are valid values

Computers

Work with IP addresses as 32
-
digit binary
numbers

30

Summary (Continued)

1 corresponds with bit that is part of network ID

0 corresponds with bit that is part of host ID

Subnetting

Takes bits from host ID and uses them as part of
network ID

Number of useable hosts on a network

Calculated with the formula 2
n
-
2

n
is the number of host bits

Supernetting

Combines multiple smaller networks into a single
larger network

Networks being combined must be contiguous