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 bits? 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 networks? 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 InterNIC.

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

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 purposes.

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 networkaddress.

Thus, in a class "A" network, 113.0.0.0 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 176.10.0.0, the broadcast address

that would be sent out to all devices on that network would be 176.10.255.255.

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 administrator.

What is included in a subnet address? Subnet addresses include a network

number, a subnet number within the

network, and a host number within the subnet.

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

How are subnet addresses created? 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 use? Subnet masks use the same format as IP

addressing. 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 portion.

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

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

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 11111111.11111111.11111110.00000000.

Therefore, 255.255.255.0 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

number.

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 subnetworks?

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

25 =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 thirty-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 197.15.22.160 on the same class "C” network. How would this be expressed in a binary numbering scheme?

Answer: If 197.15.22.160 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 197.15.22.44 wants to send data to another device attached to Cisco's network with an IP address of 131.108.2.2.

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

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 172.16.0.0. 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 255.255.255.0.

Someone outside the network sends data to the IP address 172.16.2.120.