UGC NET CSE | December 2014 | Part 2 | Question: 27

Question

In a classful addressing, first four bits in Class $A$ IP address is

• A. $1010$ 
• B. $1100$ 
• C. $1011$ 
• D. $1110$

Answer 1

In class A, the first bit of the first octet is always set to 0 (zero).

Class A 0xxx : x can be 0 or 1

Class B 10xx

Class C 110x

Class D 1110

No option is correct

Comments

same thing i was asking to you in my previous comment.

These network ID bits are used to identify the class of IP address.

and what first address you are talking about?

Please write whole ip address for example.

---

What Shiva has originally written as an answer, is correct.

Now, the arguments put forward by the other user here stands upon the misunderstanding that 1st 4 bits of 1st octet can be the lower order 4 bits of a byte, i.e.,

00000000 => 0

00000001 => 1

00000010 => 2

.

.

00001010 => 10

00001011 => 11

00001100 => 12

.

00001110 => 14

This is not what the question means by 1st four bits of Class A IP address.

Also, the other argument regarding the Network id bits, is not relevant to this question.

Now, in the above mentioned e.g. by a user,

1.1.1.1

Or,

00000001.1.1.1

Notice the Bold 0 above.

The 1st bit of the 1st octet is the MSB bit. And 1st 4 bits of the 1st octet will begin with the pattern

'0XXX'

Where X can be 0 or 1.

All the options to this question, begins with '1XXX'

Therefore, all are wrong options.

Reference link

---

sir  your answer is correct  :

First octad of Class A  has 8 bits out of which 1st Bit is used for subnetting which means network address divided into two partsi;e 0 and 1 .0 part is used in class A  and  other part for B,C

Caption

For more details click:https://youtu.be/UXMIxCYZu8o?list=PLEbnTDJUr_IegfoqO4iPnPYQui46QqT0j&t=1094

Answer 2

Answer : All    

                                      

1010 is 10 in Decimal A in Hexadecimal

1011 is 11 in Decimal B in Hexadecimal

1100 is 12 in Decimal C in Hexadecimal

1110 is 13 in Decimal D in Hexadecimal

Range of class A Network is from 0-128 in which first Ip and Last Ip address is not used as valid Ip address because they are to serve spacial purpose 

First Ip address in class A network Let say 1.0.0.0   it is having a valid no in n/w id and all 0's in host id part which indicates the network id of entire network.

Last Ip address of class A is used as Directed Broadcast Address for Exp : 2.255.255.255

Comments

Sir,

We have to take first 8 bits to find first octect number of Ip na?? Only with first 4 bits 1010 we cant say first octect is 10.

We need to take 1010xxxx to find first number.

Since first bit of all options are 1, and we need to think it as a first bit of a byte(8 bits) any given option first octect is greater than

2^7=128

Correct me plz if I am wrong

---

Sir, my understanding is like this....Please correct me if something is wrong..

---

I think shiva is right because range for class A is 0-127 why it is because 1 bit is reserved for class A I.e 0 

So we have 7 bits  with that our range is 0-127 

Here in the question , it's talking about first 4 bit 

In the first 4 bit first bit should be 0

---

@shekhar chauhan :

1110 is 14 and 1101 is 13.