• # How many subnets can you get from a network?

Subnetting. One thing that wasn't clear to me from the subnetting episode was how you figure out how many subnets you can get from a network.

I attempted the following question and got the number of hosts correct; however, I don't understand how they got the number of subnets.

Question: How many subnets and host per subnet can you get from the network 172.23.0.0 255.255.255.240?

Answer: 4096 subnets and 14 hosts per subnet

• Can you help me understand this question too. I got the number of hosts correct, but again i do not understand how the number of subnets was arrived at.
Question: How many subnets and hosts per subnet can you get from the network 172.16.0.0/18?
Answer: 4 subnets and 16,382 hosts per subnet

• Congratulations! You're doing well to get the correct answer! Thanks for the question.
I hope the answer below helps you.
Question: How many subnets and host per subnet can you get from the network 172.23.0.0 255.255.255.240?
We start with the idea of understanding that the base network is a class B network:
172.23.0.0 255.255.0.0 = 1 netowrk, 65534 possible hosts on this network.
If you now add an additional 12 bits to the network portion (the break down: 16 bits NetworkID,12 bits SubnetID, 4 bits HostID). You've taken ONE netowrk and created 2 to 12th power number of "subnets": 2^12 = 4096 networks. The remaining bits that are not associated with the network bits and subnet bits would be 4 bits for the Host bits. This gives you the 14 hosts per network. (For the host bits even if there are 16 possible combinations, we must subtract 2 -- 1 for the NetworkID, 1 for the BroadcastID).
Question: 172.16.0.0/18, how many subnets?
We start the same way: 172.16.0.0 255.255.0.0 is the base network (1 netowrk, 65534 hosts on this network). the new subnet mask= 255.255.192.0
If we add an additional 2 bits the network portion: (16 bits on base NetworkID, 2 bits as SubnetID, 14 bits as the hostID bits). So we would have 2^2 = 4 subnets we could create with each network having 2^14 = 16382 hosts per subnet.
Let us know if we need more explanation!
Cordially,
Ronnie Wong
Host, ITProTV

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