I don't understand why ip adresses are divided into network portion and host portion? is the host portion really necessary when we already have NAT?
for example, if ip addresses only have network portion, and I'm running a big company that has 1000 machines, so I can create 1000 private ip addresses, then NAT can associate thoses 1000 private ip addresses with the router internally, so any machine in my complany can be uniquely identified and can access the public internet via router, then why we still need to divde ip addresses into network portion and host portion?