How do I get the subnet ID if I have an address and mask only?
I always use a calculator (Advanced IP Address Calculator is good), but I've been trying to figure this out.
I *know* what the subnet id is (the beginning of the block), but how would I figure this out quickly?
make the conversion in binary of ip address and subnet mask
let's concentrate on 4th byte
27 = 00011011 binary
240 = 11110000 binary
then you put zeros in the host position of the mask
that leave you:
16 = 10000 binary
so the subnet address is:
Hope to help
256 - 240 (240 because of the last octet in 255.255.255.240) = 16 so subnets go up in 16
so subnet is 172.20.13.16