subnetting questions

breaker

I got this question on subnetting questions.com but I dont understand the answer.
I got 4 subnets and 62 hosts?

Question: How many subnets and hosts per subnet can you get from the network 172.23.0.0 255.255.255.192?

Answer: 1024 subnets and 62 hosts

famosbrown

You have a Class B address and a subnet mask of 255.255.255.192.

You network portion is 11111111.1111111.11111111.11000000

The first two octets are set in stone since it's Class B, so do the math on the last two octets...that gives you 1024.

Change all of the 0's to 1's and that will give you your hosts. Do the math on those.

breaker

oops, worked it out as a class c instead of b should have paid attention to the 172.

Kaminsky

Very common mistake too.

Trick is to write the subnet range as two, three octets....

In this case write it down as 0.64 and not just 64. That helped cure me.

For a class A, you would go 0.0.64 for instance. Just saying 64 will get you into no end of trouble and wasted time trying to backtrack your way out to the correct answer.