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What is IP class and number of sub-networks if the subnet mask is $255.224.0.0$?

  1. Class $A$, $3$
  2. Class $A$, $8$
  3. Class $B$, $3$
  4. Class $B$, $32$
in Computer Networks by Boss (30.8k points) | 3k views
+2
255.224.0.0

gives no of 1's followed by no. of 0's

where 1 represent network portion

here no. of 1's = 11

so, NID +SID = 11

SID =11-NID

      =11-8(class A)

      =3 bits are used for subnets

no. of sub network= 2^3-2 =6

but 6 is not in the option so in that case we consider, no. of subnets as 2^3 which is 8

answer is (B)
0
Though I also calculated answer to be option (b) but In answer key, answer given is option (A)

3 Answers

+4 votes
Best answer
Subnet mask is 11111111.11100000.00000000.00000000

here 8 bit for network ( all 8 ones )

And 8 bit for network id belong to class A

And next 3 ones used for subnet . Since 3 ones so number of subnet is 2^3=8.

So answer is b
by Loyal (9.9k points)
selected by
+3 votes
Answer B) class A ,8

 we calculate subnetwork 2^3=8
by Veteran (119k points)
–2
how can it be class A..?  

It should be class B..

ans should be between C &D
+1
@srestha sorry u r right..ans is B
+1 vote
Given mask is 255.224.0.0

No. of 1's are 11.

So no. of subnetworks = (given mask - default mask)

                                  = 11- 8 = 3

 Answer is A.
by (21 points)
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