Week 3 - IP addressing

pigeoneggtrainsNetworking and Communications

Oct 24, 2013 (3 years and 9 months ago)


Week 3

IP addressing

Introduction to IP addressing

Classes of IP addressing

Why Subnet Masks are necessary?

How to create subnet masks

Why are IP addresses written as

In order for data to pass along the media, it must first be
changed to electrical impulses.

When a computer receives these electrical impulses, it
recognizes two things: the presence of voltage on the wire
or the absence of voltage on the wire.

What format do IP addresses use?

How are IP addresses expressed
in dotted notation?

Why are IP addresses necessary?

IP addressing makes it possible for data
passing over the network media of the
Internet to find its destination.

Because each IP address is a 32
bit value,
that means that there are four billion
different IP address possibilities.

IP addresses are hierarchical addresses like
phone numbers and zip codes.

How do IP addresses make it possible for data
sent via the Internet to find its destination?

It is because each network connected to the
Internet has a unique network number.

To ensure that each network number on the
Internet will always be unique and unlike
that of any other number, an organization
called the International Network
Information Center, or InterNIC

How do IP addresses incorporate
network addresses?

Every IP address has two parts. These are known
as the network number and the host number

What are the different classes of

There are three classes of IP addresses that
a company can receive from the InterNIC.
The InterNIC reserves class "A" IP
addresses for governments throughout the
world, class "B" IP addresses for medium
size companies, and class "C"

What type of IP addressing format
does a class "A" network use?

Class A

Class B

Class C

How many classes of Networks
are there?

you have learned about three classes of
networks that can be assigned by the

In fact, there are five classes of networks.
However, only three of these are used

What IP addresses are reserved for multicast
purposes and experimental purposes?

The highest number listed was 223. You
may have wondered why the highest value
was only 223 and not 255, since there are
255 possible values for an octet.

in IP addresses the values 224 through 255
are not used in the first octet for networking

What IP addresses are reserved
for the Networks?

By convention, in IP addressing schemes,
any IP address that ends in all binary zeroes
is reserved for the network


Thus, in a class "A" network,
would be the IP address of that network.
Routers use a network's IP address when
forwarding data on the Internet.

What IP addresses are reserved
for broadcasts?

for the network that is, the broadcast address
that would be sent out to all devices on that network would

Who assigns subnet addresses?

As with the host number portion of class
"A," class "B," and class "C” addresses,
subnet addresses are assigned locally.

Usually this is done by the network

What is included in a subnet

Subnet addresses include a
, a
subnet number

within the
network, and a
host number

within the

It is by providing this third level of
addressing that subnets provide extra
flexibility for the network administrator.

How are subnet addresses

To create a subnet address, a network
administrator "borrows” bits from the host
field and designates them as the subnet field

How are subnet addresses concealed
from outside networks?

Subnets are hidden from outside networks
by using a mask.

These are referred to as subnet masks.

The function of a subnet mask is to tell
devices which part of an address is the
network number including the subnet, and
which part is the host.

What format do subnet masks

Subnet masks use the same format as IP

In other words, they are thirty two bits long
and divided into four octets.

Subnet masks have all 1s in the network and
subnetwork portion, and all 0s in the host

How many bits can be borrowed from the host
number in class "B" and class "C" networks to create

Because there are only two octets in the
host field of a class "B” network, up to
fourteen bits can be borrowed to create

A class "C" network has only one octet in
the host field. Therefore, only up to six bits
can be borrowed in class "C” networks to
create subnetworks.

What happens to the subnet mask address if only
some of the bits in an octet are borrowed?

Imagine that you have a class "B” network.
This time however, instead of borrowing all
eight bits of the third octet, only seven bits
are borrowed to create subnetworks.

Using binary representation, in this
example, the subnet mask would be

Therefore, can no longer be
used as the subnet mask.

If only seven bits are borrowed in a class "B"
network, what would the subnet mask be in dotted
decimal notation?

HINT: To convert any eight bit binary number into a
decimal number, total the powers of 2 that occur in the

What determines how many subnetworks can be
created by borrowing bits from the host field?

Can you figure out all of the possible
combinations of 0s and 1s if four bits are
borrowed from the host field to create

16 from 0000 to 1111. However, you know
that 1111 is reserved for broadcast and 0000
means this network.

How many subnetworks can be created by
borrowing five bits from the host field?

Answer: Thirty
two subnetworks or

=32 subnetworks can be created by
borrowing five bits from the host field.

Which numbers in a subnetwork
are reserved for broadcasts?

In previous section, we used an example of a class
"C" network in which three bits are borrowed
from the host field. You learned that when three
bits are borrowed from the host octet, up to eight
subnetworks can be created each having up to
two hosts.

You also learned that IP addresses ending in all
binary 1s are reserved for broadcasts. The same is
true for subnetworks.

For IP address on the same class "C”
network. How would this be expressed in a binary
numbering scheme?

Answer: If is converted to
binary format, it becomes
110001010.00001111.00010110. 10100000.

The first three bits in the last octet, 101,
indicate that this is the sixth subnetwork. As
before the remaining bits are all binary 0s.
This means that the IP
address197.15.22.160 must be one that is
reserved for a subnetwork address.

How does the router handle IP
addresses and subnet masks?

Let's assume that a device on another network
with an IP address of wants to send
data to another device attached to Cisco's network
with an IP address of

The data is sent out over the Internet until it
reaches the router that is attached to Cisco's

The router's job is to determine which one of
Cisco's subnetworks the data should be routed to.

when the router performs this ”ANDing"
operation, the host portion falls through

The router looks at what is left which is the
network number including the subnetwork.

The router then looks in its routing table and tries to
match the network number including the subnet with
an interface.

How does the "Anding” operation
change with different subnet masks?

Imagine that you have a class "B” network with
the network number

After assessing the needs of his network, the
network administrator has decided to borrow eight
bits in order to create subnetworks.

When eight bits are borrowed to create subnets,
the subnet mask is

Someone outside the network sends data to the IP