 UGC NET Computer Science Question Solution June- 2019 -Paper -II Explanation:

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Classful IP addresses is divided into classes. The leading bits of classes are:
Class A – 0
Class B – 10
Class C – 110
Class D – 1110
Class E – 1111

On the basis of percentage, address space consume by all classes are:
Class A – 50%
Class B – 25%
Class C – 12.5%
Class D – 6.25%
Class E – 6.25% Explanation:

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We know,
In a Class B network, the first 16 bits are the network part of the address. & remaining 16 bits indicate the host within the network.

A subnet mask always consists of a series of contiguous 1 bits followed by a series of contiguous 0 bits.Where,
• 1’s represent Network ID & Subnet ID
• 0’s represent Host ID

Given that,
Number of Subnet = 500 subnet
So, Number of bits required to represent subnet = ceil value of(500) = 9bits

Number of Host per subnet = 100 subnet
So, Number of bits required to represent subnet = ceil value of(100) = 7 bits

Now,
We borrow 9bits of Subnet ID bits from Host ID part(16 bits is HID part in class B) to represent 500 subnet.
Network ID bits = 16 bits
Subnet ID bits = 9 bits
Host ID bits = 16-9 = 7bits

Now its obvious,
Number of 1’s in subnet mask = Network ID bits + Subnet ID bits = 16 + 9 = 25
Number of 0’s in subnet mask = Host ID bits = 7

1111 1111 . 1111 1111 . 1111 1111 . 1000 0000
In decimal form it is represented as:
255 : 255 : 255 : 128

So, Option(II) is correct.

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ARP :
• Address Resolution Protocol [ARP] is a network layer protocol that is used to convert IP address into MAC address.

DNS:
• DNS stands for Domain Name System.
• DNS is a service that translates the domain name into IP addresses.
• For example, the domain name www.samagraCS.com has a IP address 162.0.215.21(Suppose)
• Where, www is a particular host server.
• The com part of the domain name reflects the purpose of the organization or entity (in this example, commercial) and is called the top-level domain name.
• The samagraCS part of the domain name defines the organization and together with the top-level is called the second-level domain name.

RARP:
• Reverse Address Resolution Protocol (RARP) is a network layer protocol used to convert an IP address from a given physical address.
• RARP is the complement of ARP.

ICMP:
• The ICMP stands for Internet Control Message Protocol.
• ICMP is a network level protocol.
• ICMP (Internet Control Message Protocol) is an error-reporting protocol that network devices such as routers use to generate error messages to the source IP address when network problems prevent delivery of IP packets.

So, Option(III) is correct.

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• A loopback address is a special IP address, 127.0.0.1, reserved by InterNIC for use in testing network cards.
• A loopback address works is that a data packet will get sent through a network and routed back to the same device where it originated.
• In IPv4, 127.0.0.1 is the most commonly used loopback address, however, this can range be extended to 127.255.255.255.
The loopback (IP) address is used to send a packet from host to itself & check NIC working or not.
• The loopback (IP) address is a member of class A network. (IP Address of Class A network range from 0.0.0.0 to 127.255.255.255)

Statement P: The loopback(IP) address is a member of class B network (False).
Because, The loopback(IP) address is a member of class A network.

Statement Q: The loopback(IP) address is used to send a packet from host to itself (True)

So, Option(II) is correct.

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Given :
Bandwidth (Bw) = 1Gbps = 109 bps
Link Length or Distance (d) = 800 Km
Speed or velocity (v) = 200,000 Km / Sec

Propogation Delay: It is a measure of the time required for asignal to propogate from one end of circuit to other end.

Formula used : Calculation:  = 0.004 sec
= 4 ms

{1 second = 1000 millisecond}

So, Option(IV) is correct.

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