we need sub netting for two reasons
2. good use of public ip addresses
for webhosting companies subnetting is really important, because they sell ip address.
When the nw ids are different then the ip address will communicate through a router. For example 10.0.5.1/24 can communicate to 188.8.131.52/24 can not communicate directly, as the network id is different, so they will have to go through routers
step1: write down the default mask.
step2: find out how many bit we need to borough 4bit->16networks. The boroughed one will become 1s and rest zero.
step3: How many zeros we have.