Answers: How Many Subnets/Hosts 1
Remember last Friday’s speed practice? Sorry for the delay in posting the answers. They are below the fold. As usual, I’ve listed the answers, but if it’s not clear why, you need to ask, so please do so. And sorry for the delay.
To answer these questions, you need to make two assumptions:
1) that the same mask is used for all subnets
2) that the zero subnet and broadcast subnet are allowed
Without the first assumption, you simply cannot determine the number of subnets. Without the second assumption, you cannot determine whether you need to subtract 2 from the total (if those two special subnets are not allowed), or not.
With those assumptions, all you have to do is determine the number of network, subnet, and host bits. You already know the prefix mask (/P) per each problem statement. From there:
a) Determine the number of network bits per class A, B, and C rules
b) Determine the number of subnet bits (S), which is the different between the prefix (P) and network bits (N): S = P – N
c) Determine the number of host bits, which is 32 – P.
Here are the answers to this set of questions.
| Class | Network Bits (N) | Subnet Bits (S = P – N) | Host Bits (32 – P) | |
|
1 |
A |
8 |
9 |
15 |
|
2 |
A |
8 |
13 |
11 |
|
3 |
B |
16 |
6 |
10 |
|
4 |
C |
24 |
3 |
5 |
|
5 |
C |
24 |
6 |
2 |
|
|
Number of Subnets |
Number of Hosts |
|
1 |
2^9 = 512 |
2^15 – 2 = 32,766 |
|
2 |
2^13 = 8192 |
2^11 – 2 = 2046 |
|
3 |
2^6 = 64 |
2^10 – 2 = 1022 |
|
4 |
2^3 = 8 |
2^5 – 2 = 30 |
|
5 |
2^6 = 64 |
2^2 – 2 = 2 |