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Kurose's TopDown Network book says:

8.7.1 IPsec and Virtual Private Networks (VPNs)

An institution that extends over multiple geographical regions often desires its own IP network, so that its hosts and servers can send data to each other in a secure and confidential manner. To achieve this goal, the institution could actually deploy a stand-alone physical network - including routers, links, and a DNS infrastructure

  • that is completely separate from the public Internet. Such a disjoint network, dedi- cated to a particular institution, is called a private network. Not surprisingly, a private network can be very costly, as the institution needs to purchase, install, and maintain its own physical network infrastructure.

Instead of deploying and maintaining a private network, many institutions today create VPNs over the existing public Internet. ...

So a private network is what VPN tries to simulate.

Is a private network the same concept as a network which uses private IP addresses inside it?

If not, does a private network necessarily use the following private IP addresses inside it:

10.0.0.0 - 10.255.255.255/8 (16,777,216 hosts)
172.16.0.0 - 172.31.255.255/12 (1,048,576 hosts)
192.168.0.0 - 192.168.255.255/16 (65,536 hosts)

Is a private network isolated from its outside? Can a host in it communicate with a host outside it? If yes, is it done by NAT? (A network which uses private IP addresses inside it can communicate with its outside, and that can be done by NAT.)

Thanks.

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Depending on the context and your own preference, a private network is usually one that uses private network addresses. The term may also be any network that is not open to the public to route into or through.

Most private networks use private addresses for IPv4 (or ULA for IPv6) but networks without connection to the public Internet can actually use any addresses they want (making that connection later on will become a challenge though).

is a private network isolated from its outside?

Some are.

Can a host in it communicate with a host outside it?

Not if the network is isolated. Yes if network connectivity and security policies allow.

If yes, is it done by NAT?

Either NAT or some proxy scheme (off topic here).

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  • Thanks. How would you define a network being a private one?
    – Tim
    Dec 5, 2023 at 7:07
  • A private network is usually one that uses private network addresses. The term may also be any network that is not open to the public to route into or through.
    – Zac67
    Dec 5, 2023 at 7:36
  • (1) Does "usually" mean that "uses private network addresses" isn't a character of a private network? (2) Is "not open to the public to route into or through" a character or even a defining one of a private network? If yes, how can VPN help people living under Internet censorship access the Internet, if what it simulates is "not open to the public to route into or through"?
    – Tim
    Dec 5, 2023 at 7:51
  • You're straying off topic here and it's becoming a whole different question - but as far as we can go: if you throw a cable over to your neighbor or open your Wifi for them, that's a private network.
    – Zac67
    Dec 5, 2023 at 8:02
  • I am staying on the question of what a private network is
    – Tim
    Dec 5, 2023 at 8:08

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