Question

Given a network address... 10.0.0.0 /16

Using no calculators, how would I calculate the subnet number for the 128th Subnet?

Please help, final in 12 hours!

Answer 1

I'm not 100% sure on this, so please correct me if I'm wrong.

An IPv4 address is 32 bits long. The specification of 10.0.0.0/16 indicates that the network address is 16 bits long. Therefore, the network address is 16 bits long and the subnet number is (32-16=) 16 bits long as well.

An IPv4 address contains four `octets' (an octet is eight bits) that are separated by dots. Thus the first two octets in the IP address (10.0) will be the network address and the last two octets (0.0) will be the subnet number. To determine the proper subnet number of the xth subnet, you will need to either convert x to binary, split the two sets of eight bits and convert those back to decimal numbers, or you will need to divide x by 256 to determine the first octet and then determine the modulo of x and 256 to determine the second octet.

Answer 2

You have the correct process. I ended up getting 100% on the practical final, which would have involved this question. Thankfully, the prof didn't use it - as it is sort of an unnecessary process given the availability of calculators in the real world.

I appreciate the response regardless, what a cool site!