How to calculate a subnet mask from IP address?

Question

I just want to understand how this software works: http://www.subnet-calculator.com/

Answer 1

Just use bing/google :(

After two seconds searching i found this I know it's not perfect, but you can probably find something better. This topic should be documented well on the net.

Answer 2

It's not really calculating the address mask from the address. Rather it's calculating the network mask, address, number of sub-nets and size of each subnet from the class of network you supply (A, B or C). Most of this is defined in RFC 1918 (see §3 in particular).

Answer 3

You can't calculate the subnet mask from the ip address. You calculate the subnets (ips range) from the subnet mask by performing a bitwise AND with the ip address.

So for example, with a subnet mask of 255.255.255.0 only the fourth part of an ip address can vary, resulting in 255 possible addresses for 192.168.0.x.

Sorry for the lack of precise vocabulary, this was quite a quick and dirty explanation... Wikipedia has a better one.

Answer 4

Here is a simple tutorial IP subnetting made easy