I don't understand the meaning of the network part in private IP and global IP

Question: Question:


I'm looking into IP addresses, but it's difficult to tell whether the information I've looked up is a global IP or a private IP, and I'm confused.
I have summarized the questions below, and I would appreciate it if you could answer.

I'm sorry that I don't understand this matter well and I can't ask good questions.


Network part in the only one network

Consider a network in which four devices are connected to one router.
There is only one network in this situation.
And even if there is no network part, if you assign a unique private IP in the router to each device, you should be able to route without problems.
Then why is the concept of network part necessary in this private network?

Network configuration for separating multiple networks

Consider the same network situation as above.
In this situation, what kind of network configuration should be used to divide the network into multiple parts and make the network part function?


Is CIDR a concept for private IP or global IP? (Or both?)
If it also applies to global IP, what does the network part of global IP mean?

Network part of global IP

Global IP is uniquely defined worldwide.
In other words, routing is possible without the concept of a network part.
Why does the idea of ​​a network department exist?

Answer: Answer:

Then why is the concept of network part necessary in this private network?

Not necessary as you pointed out. The assumed network does not require a router in the first place, a switching hub is sufficient. And if it is a switching hub, not only the network part but also the network setting is not required.
Other devices request the settings of the network part only to match the existing functions by diverting the existing network products.

Is CIDR a concept for private IP or global IP?

Neither. It is a standard to judge whether it is inside or outside the network. If the network part of the communication partner and your own network part match, it is judged that you are in the same network and you can communicate directly without going through a router. If the network parts do not match, it is out of the network and communication is performed via the router.

As mentioned above, private / global is irrelevant.

Routing is possible without the concept of a network part.

There is a leap of logic. It does not matter that the address is unique and that it is physically reachable to the other party. Of course, it is reachable if all the devices in the world are receiving the communication of all the devices (that is, if the whole world is the network configuration of the first question), but it is not feasible due to the network load. ..

In the real world, as mentioned above, communication is performed directly within the network, and communication is performed via a router outside the network. You can understand how the routers in each network are connected by reading the explanations such as EGP / IGP and BGP .

As you may have noticed in the explanation so far, the term "routing" refers to the very judgment of the route to communicate with the communication partner. And the first step in that decision is whether the network parts match.

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