## IP Address in Networking | Problems

Before you go through this article, make sure that you have gone through the previous article on IP Address.

We have discussed-

• IP Address is a unique address assigned to each computing device in an IP network.
• ISP assigns IP Address to all the devices present on its network.
• Casting refers to transmitting data (stream of packets) over the network.

## Point-01:

• If the range of first octet is [1, 126], then IP Address belongs to class A.
• If the range of first octet is [128, 191], then IP Address belongs to class B.
• If the range of first octet is [192, 223], then IP Address belongs to class C.
• If the range of first octet is [224, 239], then IP Address belongs to class D.
• If the range of first octet is [240, 254], then IP Address belongs to class E.

## Point-02:

• IP Address of its network is obtained by setting all its Host ID part bits to 0.

## Point-03:

• Direct Broadcast Address is obtained by setting all its Host ID part bits to 1.

## Point-04:

• For any given IP Address, limited Broadcast Address is obtained by setting all its bits to 1.

## Point-05:

• Class D IP Addresses are not divided into Net ID and Host ID parts.
• Class E IP Addresses are not divided into Net ID and Host ID parts.

## Problem-01:

1. 1.2.3.4
2. 10.15.20.60
3. 130.1.2.3
4. 150.0.150.150
5. 200.1.10.100
6. 220.15.1.10
7. 250.0.1.2
8. 300.1.2.3

## Part-A:

1.2.3.4

• IP Address belongs to class A
• Network IP Address = 1.0.0.0

## Part-B:

10.15.20.60

• IP Address belongs to class A
• Network IP Address = 10.0.0.0

## Part-C:

130.1.2.3

• IP Address belongs to class B
• Network IP Address = 130.1.0.0

## Part-D:

150.0.150.150

• IP Address belongs to class B
• Network IP Address = 150.0.0.0

## Part-E:

200.1.10.100

• IP Address belongs to class C
• Network IP Address = 200.1.10.0

## Part-F:

220.15.1.10

• IP Address belongs to class C
• Network IP Address = 220.15.1.0

## Part-G:

250.0.1.2

• IP Address belongs to class E
• Network IP Address = Not available

## Part-H:

300.1.2.3

• This is not a valid IP Address.
• This is because for any given IP Address, the range of its first octet is always [1, 254].
• First and Last IP Addresses are reserved.

## Problem-02:

A device has two or more IP Addresses, the device is called-

1. Workstation
2. Router
3. Gateway
4. All of these

## Solution-

• All the given devices have a network layer.
• So, they will have at least one IP Address.

In TCP/IP suite-

• Workstation and gateway have all the 5 layers.
• Router has only 3 layers last layer being network layer.

## Workstation-

• A user may configure more than one IP Addresses in his workstation / computer.
• With more than one IP Address, it remains present in more than one networks.
• So, if one network goes down, it is always reachable from other networks.

The following figure shows a host present in more than one networks-

• It is important to note that IP Addresses are assigned to interfaces.
• When we buy a new laptop, we usually get 2-3 interfaces.
• Thus, a workstation can have more than one IP Addresses.

## Router-

• A router may be connected to various interfaces.
• Each interface has a unique IP Address.
• Thus, a router may also have more than IP Addresses.
• Similar is the case with gateways because gateways are extension of routers.

Thus, Option (D) is correct.

## Problem-03:

A host with IP Address 200.100.1.1 wants to send a packet to all the hosts in the same network.

What will be-

## Solution-

1. Source IP Address = IP Address of the sender = 200.100.1.1

## Problem-04:

A host with IP Address 10.100.100.100 wants to use loop back testing.

What will be-

## Solution-

• Source IP Address = 10.100.100.100

## Problem-05:

How many bits are allocated for Network ID and Host ID in 23.192.157.234 address?

## Solution-

Given IP Address belongs to class A.

Thus,

• Number of bits reserved for Network ID = 8
• Number of bits reserved for Host ID = 24

## Problem-06:

Which devices can use logical addressing system?

1. Hub
2. Switch
3. Bridge
4. Router

## Solution-

• Devices which have network layer as the last layer can only use logical addressing system.
• Devices which have data link layer as the last layer can only use physical addressing system.

### Option-A:

• Hub can neither use physical addressing system nor logical addressing system.
• This is because it has physical layer as the last layer.

### Option-B:

• Switch can use physical addressing system but not logical addressing system.
• This is because it has data link layer as the last layer.

### Option-C:

• Bridge can use physical addressing system but not logical addressing system.
• This is because it has data link layer as the last layer.

### Option-D:

• Router can use physical addressing system as well as logical addressing system.
• This is because it has network layer as the last layer.

Thus, option (D) is correct.

## Problem-07:

What is the network ID of the IP Address 230.100.123.70?

## Solution-

• Given IP Address belongs to class D.
• Class D IP Addresses are not divided into the Network ID and Host ID parts.
• Thus, there is no network ID for the given IP Address.

## Problem-08:

Match the following-

#### Column-I:

1. 200.10.192.100
2. 7.10.230.1
3. 128.1.1.254
4. 255.255.255.255
5. 100.255.255.255

1. Class A
4. Class C
5. Class B

## Solution-

(I, D), (II, A), (III, E), (IV, B), (V, C)

## Problem-09:

Suppose that instead of using 16 bits for network part of a class B Address, 20 bits have been used. How many class B networks would have been possible?

## Solution-

• Total 20 bits are used for Network ID of class B.
• The first two bits are always set to 10.
• Then, with 18 bits, number of networks possible = 218

## Problem-10:

What is the default mask for 192.0.46.10?

## Solution-

• Given IP Address belongs to class C.
• For class C, default mask = 255.255.255.0

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In networking,

• It is a unique address assigned to each computing device in an IP network.
• ISP assigns IP Address to all the devices present on its network.
• Computing devices use IP Address to identify and communicate with other devices in the IP network.

IP Addresses may be of the following two types-

• Static IP Address is an IP Address that once assigned to a network element always remains the same.
• They are configured manually.

### NOTE

• Some ISPs do not provide static IP addresses.

• Dynamic IP Address is a temporarily assigned IP Address to a network element.
• It can be assigned to a different device if it is not in use.
• DHCP or PPPoE assigns dynamic IP addresses.

• IP Address is a 32 bit binary address written as 4 numbers separated by dots.
• The 4 numbers are called as octets where each octet has 8 bits.
• The octets are divided into 2 components- Net ID and Host ID.

1. Network ID represents the IP Address of the network and is used to identify the network.
2. Host ID represents the IP Address of the host and is used to identify the host within the network.

Example of an IP Address is-

00000001.10100000.00001010.11110000

(Binary Representation)

OR

1.160.10.240

(Decimal Representation)

There are two systems in which IP Addresses are classified-

In Classful Addressing System, IP Addresses are organized into following 5 classes-

1. Class A
2. Class B
3. Class C
4. Class D
5. Class E

## 1. Class A-

 If the 32 bit binary address starts with a bit 0, then IP Address belongs to class A.

• The first 8 bits are used for the Network ID.
• The remaining 24 bits are used for the Host ID.

### Total Number Of IP Addresses-

Total number of IP Addresses available in class A

= Numbers possible due to remaining available 31 bits

= 231

### Total Number Of Networks-

Total number of networks available in class A

= Numbers possible due to remaining available 7 bits in the Net ID – 2

= 27 – 2

= 126

(The reason of subtracting 2 is explained later.)

### Total Number Of Hosts-

Total number of hosts that can be configured in class A

= Numbers possible due to available 24 bits in the Host ID – 2

= 224 – 2

(The reason of subtracting 2 is explained later.)

### Range Of 1st Octet-

We have-

• Minimum value of 1st octet = 00000000 = 0
• Maximum value of 1st octet = 01111111 = 127

From here,

• Range of 1st octet = [0, 127]
• But 2 networks are reserved and unused.
• So, Range of 1st octet = [1, 126]

## Use-

• Class A is used by organizations requiring very large size networks like NASA, Pentagon etc.

## 2. Class B-

 If the 32 bit binary address starts with bits 10, then IP Address belongs to class B.

• The first 16 bits are used for the Network ID.
• The remaining 16 bits are used for the Host ID.

### Total Number Of IP Addresses-

Total number of IP Addresses available in class B

= Numbers possible due to remaining available 30 bits

= 230

### Total Number Of Networks-

Total number of networks available in class B

= Numbers possible due to remaining available 14 bits in the Net ID

= 214

### Total Number Of Hosts-

Total number of hosts that can be configured in class B

= Numbers possible due to available 16 bits in the Host ID – 2

= 216 – 2

### Range Of 1st Octet-

We have-

• Minimum value of 1st octet = 10000000 = 128
• Maximum value of 1st octet = 10111111 = 191

So, Range of 1st octet = [128, 191]

## Use-

• Class B is used by organizations requiring medium size networks like IRCTC, banks etc.

## 3. Class C-

 If the 32 bit binary address starts with bits 110, then IP Address belongs to class C.

• The first 24 bits are used for the Network ID.
• The remaining 8 bits are used for the Host ID.

### Total Number Of IP Addresses-

Total number of IP Addresses available in class C

= Numbers possible due to remaining available 29 bits

= 229

### Total Number Of Networks-

Total number of networks available in class C

= Numbers possible due to remaining available 21 bits in the Net ID

= 221

### Total Number Of Hosts-

Total number of hosts that can be configured in class C

= Numbers possible due to available 8 bits in the Host ID – 2

= 28 – 2

### Range Of 1st Octet-

We have-

• Minimum value of 1st octet = 11000000 = 192
• Maximum value of 1st octet = 110111111 = 223

So, Range of 1st octet = [192, 223]

## Use-

• Class C is used by organizations requiring small to medium size networks.
• For example- engineering colleges, small universities, small offices etc.

## 4. Class D-

 If the 32 bit binary address starts with bits 1110, then IP Address belongs to class D.

• Class D is not divided into Network ID and Host ID.

### Total Number Of IP Addresses-

Total number of IP Addresses available in class D

= Numbers possible due to remaining available 28 bits

= 228

### Range Of 1st Octet-

We have-

• Minimum value of 1st octet = 11100000 = 224
• Maximum value of 1st octet = 11101111 = 239

So, Range of 1st octet = [224, 239]

## Use-

• Class D is reserved for multicasting.
• In multicasting, there is no need to extract host address from the IP Address.
• This is because data is not destined for a particular host.

## 5. Class E-

 If the 32 bit binary address starts with bits 1111, then IP Address belongs to class E.

• Class E is not divided into Network ID and Host ID.

### Total Number Of IP Addresses-

Total number of IP Addresses available in class E

= Numbers possible due to remaining available 28 bits

= 228

### Range Of 1st Octet-

We have-

• Minimum value of 1st octet = 11110000 = 240
• Maximum value of 1st octet = 11111111 = 255

So, Range of 1st octet = [240, 255]

## Use-

• Class E is reserved for future or experimental purposes.

All the classes of IP Address are summarized in the following table-

 Class of IP Address Total Number of IP Addresses 1st Octet Decimal Range Number of Networks available Hosts per network Default Subnet Mask Class A 231 1 – 126 27 – 2 224 – 2 255.0.0.0 Class B 230 128 – 191 214 216 – 2 255.255.0.0 Class C 229 192 – 223 221 28 – 2 255.255.255.0 Class D 228 224 – 239 Not defined Not defined Not defined Class E 228 240 – 254 Not defined Not defined Not defined

## Note-01:

• All the hosts in a single network always have the same network ID but different Host ID.
• However, two hosts in two different networks can have the same host ID.

## Note-02:

• A single network interface can be associated with more than one IP Address.

## Note-03:

• There is no relation between MAC Address and IP Address of a host.

## Note-04:

• IP Address of the network called Net ID is obtained by setting all the bits for Host ID to zero.

## Note-05:

• Class A Networks accounts for half of the total available IP Addresses.

## Note-06:

 In class A, total number of IP Addresses available for networks are 2 less.

• This is to account for the two reserved network IP Addresses 0.xxx.xxx.xxx and 127.xxx.xxx.xxx.
• IP Address 127.0.0.1 is reserved for loopback address used for software testing.

## Note-07:

 In all the classes, total number of hosts that can be configured are 2 less.

• This is to account for the two reserved IP addresses in which all the bits for host ID are either zero or one.
• When all Host ID bits are 0, it represents the Network ID for the network.
• When all Host ID bits are 1, it represents the Broadcast Address.

## Note-08:

• Only those devices which have the network layer will have IP Address.
•  So, switches, hubs and repeaters does not have any IP Address.