IP Addressing And Subnetting : MCQs & PYQs with Explanation

Option B

When an IP address is written with CIDR notation, such as 205.16.37.39/28, it tells us that the first 28 bits represent the network part, and the remaining 4 bits represent the host part of the address. 
Since 4 bits are reserved for hosts, the total number of addresses in this subnet is 2⁴=16. These addresses include both the network address and the broadcast address.

To find the exact block range, we must identify where the given IP (205.16.37.39) falls. Subnets with a /28 prefix have a block size of 16, and the subnets start at multiples of 16 in the last octet. Thus, the valid subnet ranges in the fourth octet are 0–15, 16–31, 32–47, 48–63, and so on. The number 39 lies between 32 and 47, which means the network address is 205.16.37.32.

Since the subnet contains 16 addresses, they run sequentially from 205.16.37.32 to 205.16.37.47. The first address 205.16.37.32 is reserved as the network address, and the last address 205.16.37.47 is reserved as the broadcast address for this subnet.

Option C

In IPv4, when a packet is too large to be transmitted in one piece, it may be fragmented into smaller packets. Each fragment carries two important fields:

1. Fragment Offset indicates the position of the fragment’s data in the original packet.
2. MF (More Fragments) flag indicates whether more fragments follow (1 indicates more fragments, 0 indicates last fragment).

If a packet has Fragment Offset = 0 and MF = 0, it means that there are no fragments before or after it. A Fragment Offset of 0 shows it is the first fragment, but since MF = 0 indicates no more fragments, the packet must be unfragmented and sent as a single complete datagram.

Option A

In CIDR (Classless Inter-Domain Routing) notation, the suffix “/24” denotes that 24 bits are used for the network part of the IP address. This means that the first 24 bits out of the total 32 bits in an IPv4 address identify the network, while the remaining 8 bits are used for host addresses within that network.
The "/24" notation corresponds to a subnet mask of 255.255.255.0 in traditional dotted decimal format. It essentially tells how many bits are fixed for the network prefix, allowing flexible subnetting and efficient allocation of IP address space.

Option B

IP addressing is used to uniquely identify devices on a network. In IPv6, the address size was increased to overcome the limitations of IPv4 (32-bit). IPv6 uses a 128-bit address, allowing a very large number of unique IP addresses.

Option B

In IPv4, the address range 127.0.0.0 to 127.255.255.255 is reserved for loopback communication. 
A loopback address is used when a computer needs to communicate with itself. The data sent to a loopback address does not go to another device on the network. Instead, it is returned to the same computer.
The most commonly used loopback address is 127.0.0.1, which is often called localhost.

Option B

Private IP addresses are reserved ranges used within local networks. For Class C, the private IP range is 192.168.0.0 to 192.168.255.255.
The IP address 192.168.24.43 falls within this range, so it is a valid Class C private IP address.

Private IP Address Ranges:

Option C

In IPv4, an IP address can be used as a source address or a destination address. A source address identifies the device sending the packet and is normally a unicast address. 
A destination address can be unicast, multicast, or broadcast, depending on whether the packet is intended for one device, a group of devices, or all devices on the network.
Option (C) is false because a multicast address is not a special case of a broadcast address. They have different purposes. 
A broadcast sends data to all devices in the relevant broadcast domain, while a multicast sends data only to devices that have joined a particular multicast group.

• In IPv4, the limited broadcast address is 255.255.255.255, where all 32 bits are 1.
• Multicast Addresses belong to Class D, ranging from 224.0.0.0 to 239.255.255.255.

Option B

To create subnets in a Class B network, we start with the default subnet mask 255.255.0.0. The organization wants 64 departments, which means they need 64 subnets. To find how many bits are needed for subnetting, we check powers of two, i.e., 2ⁿ ≥ 64.
When we try 2⁶, we get 64, which matches the requirement. This means the network must borrow 6 bits from the host portion to create the subnets.
In a Class B address, the subnetting begins in the third octet. When we borrow 6 bits, the first 6 bits of the third octet become 1s. In binary, these 6 ones followed by two zeros give the value 252.
255.255.11111100.00000000

So, the subnet mask becomes, 255.255.252.0

Option C

The company requires confidentiality and integrity of transmitted data, and the private IP addresses inside the company must also remain hidden.
In IPSec, ESP (Encapsulating Security Payload) provides encryption, confidentiality, and data integrity, while AH (Authentication Header) provides only authentication and integrity but no encryption. Therefore, AH cannot ensure confidentiality.
Additionally, Tunnel Mode encrypts the entire original IP packet including the original IP header, which hides the private IP addresses of internal systems. In contrast, Transport Mode encrypts only the payload, leaving the original IP header visible.
Thus, to achieve both encryption and protection of internal IP addresses, the correct configuration is IPSec using ESP in Tunnel Mode.

Option C

To find the network address, we perform a bitwise AND operation between the IP address and the subnet mask.
Given:

• IP Address = 172.16.100.11
• Subnet Mask = 255.255.255.0

The subnet mask 255.255.255.0 means the first three octets represent the network part, and the last octet represents the host part. So, applying AND operation:

• First three octets remain the same : 172.16.100
• Last octet becomes 0 : 0

Thus, the network address is 172.16.100.0.