subnets

Question

The network address of 172.16.0.0/19 provides how many subnets and hosts?

A. 7 subnets, 30 hosts each B. 8 subnets, 8,190 hosts each C. 8 subnets, 2,046 hosts each   7 subnets, 2,046 hosts each pls tel me hw to solve this

Answer 1

Answer : B

Here 19 shows the Network Id part

This is a Class B address, so that is why here  only 3 sub-net bits, How  172.16.0.0 ===> 172.16.000 | 00000.00000000 

Before straight line in above address are the N/w id in which 3 bits are for sub-net. 

with 3 bits we got 2^3 =8 Sub-nets . And with 13 host bits we got 2^13 = 8192 Hosts per Network In which we are not going to consider the First and Last Ip address So Total Hosts going to be 8190

Answer 2

!st of all....you need to know that what is 19 over here ...

19 is the number of 1's present in the subnet mask for this address 

A CIDR address of /19 is 255.255.224.0. i.e. 11111111.11111111.11100000.000000000 . This is a Class B address, so there is only 3 subnet bits, but it provides 13 host bits, or 8 subnets, each with 8,190 hosts.

->The host's formula is (2n - 2) where n is the number of host bits 

->Number of subnets = 2^n where n is the number of bits borrowed to make the subnet mask

Experts Kindly add more relevant points to make students understand & correct me If I am worng

Answer 3

As per my understanding this question is not correct..There should be an option of  None of these 

As subnet bit according to CIDR notation is =3

so no.of subnets = (2^n-2)(as 000 and 111 is excluded because they represent the case of net.id and DBA)

= 6

and no.of host bit = 13

so no of hosts= (2^n-2)(00000.00000000 and 11111.255 is excluded for same reason)

=8190