I am trying to understand the addressing strategies. But there is something which I can't grasp. Maybe I am missing a very basic point, if so, I am sorry beforehand.
From my researches, let's say, if a company wants 100,000 IP addresses for their network, Class C won't cut it since Class C can allocate 256 addresses. Same for Class B since it can allocate 65,536 addresses. So they were asking for Class A which can allocate 16,777,216 addresses but that would be a huge waste of IP addresses.
Now coming to my question. Don't all computers in a company reside behind a public IP address configured by a router? Let's say I have one router for an office in Istanbul which has 185.245.32.78 as the public IP address. All the computers in that office would have 192.168.xxx.xxx as private IP addresses. The same for other offices. I could use 20 different public IP addresses for other offices spreading around the world and have same private IP addresses behind a routers.
Doesn't this mean I could have many offices with networks with only Class C allocation?
Best Answer
You are confusing the typical home networking setup, which is off-topic here. with a business network. Many businesses have multiple services (often the same type of service provided by different servers), and they need public addressing for each server.
Under your example, a company with multiple web servers for different functions would have a single public address, and TCP port 80 (HTTP) for that single public address could only be forwarded to one of those servers.
The original premise of IP is that each host gets a unique address. The version of NAT (NAPT) that allows a network to hide behind a single public address only works with ICMP, TCP, and UDP. Other transport protocols are broken by NAPT, and even some application-layer protocols that use TCP or UDP are broken by NAPT.