What is a Subnet Calculator good for? Well for 99% of Internet users it is of no importance. So if you don't know what a subnet is this is probably not the Calculator for you.
A Internet address is a set of numbers like 192.168.0.1. A Internet address is actually a 32bit Integer. The address is divided into two parts, the network number and the host number. The net mask is used to show the Network number. In the old days there where only three net masks 255.0.0.0 255.255.0.0 and 255.255.255.0 for A,B and C class networks. With the increasing number of hosts on the Internet a more effective scheme is used called Classless Inter-Domain Routing (CIDR). With CIDR you decide how many bits are being used for the network part. A old Class C address (255.255.255.0) is in CIDR notation /24 (i.e. the first 24 bits of the address is used for the network number)
The Subnet calculator start of with mask /25. If you are using 25 bits, your subnet mask is (check the lower part of the tool) 255.255.255.128, you can divide a old Class C network into two parts. Now slide the network address slider past 127, you will see that the Network Address changed from 192.168.0.0 to 192.168.0.128. You can also see that the broadcast address changed. If you want to make a list of all possible CIDR networks from the chosen mask/address press the Generate subnet list. Hopefully this will give you an idea of how sub netting works Try out our online Subnet calculator, pull the sliders to see how the number of hosts per subnet changes
So what is all this IPv6 hype? As more and more toasters are getting online, the world has run out of IP adresses (or rather the old type IPv4). To be able to let more toasters, smartphones and other devices online a new type of ip addresses are used IPv6. IPv6 adresses are 128bits long instead of 32. IPv6 support in subnet calc? Not quite yet, but if demand exists of course we will fix it.