I *finally* understand subnetting..... well, most

FLEOHB

I have spent the last month and a half (4 days a week)trying to understand subnetting. After studying today I finally got most of it. The questions that are;

What is the last valid host on the subnetwork 172.29.106.64 255.255.255.192?

And questions like it I understand, what I am having a hard time with is questions like;

How many subnets and hosts per subnet can you get from the network 172.30.0.0/23?

Is there a easy way to work those questions out or do I just need to start memorizing a lot of numbers?

*all example questions taken from subnettingquestions.com

GeeGeez0rz

Ok, just had a look at this one, so.. (im bad at explaining, but ill try)

Its a class B address and the "subnetting" is happening in the 3rd octet. The number of bits being taken from the hosts and added to the network portion is 7. So 2^7 = 128

With the hosts its 2^9-2 (as we now only have 9 bits for the hosts and we take away two for broadcast and network) so that leaves us 510 hosts per subnet.

172.30.0.0
255.255.254.0

2^7 = 128 subnets
2^9-2 = 510 hosts

The way i remember the powers of 2 is i start from 256, i know 2^8 = 256. So all i need to do is remember that one, and I can work up or down. Saves memorising a ton of numbers.

I hope this helps, but im sure someone will be able to explain much better.