private IP addresses

IP address exhaustion problem

 Some IP addresses are reserved. Among the special IP addresses, I will explain the private IP address.

*The story here is IPv4.

In addition, since the IP address consists of 32 bits,

 2 32  = 4,294,967,296

It turns out that there are about 4.3 billion IP addresses.

 This sounds like enough IP addresses, but given the world's population (6.6 billion as of January 2008), there's not even one IP address per person. Moreover, it is not possible to assign one IP address to one computer.

 In the first place, when IP addresses were initially allocated, they were roughly allocated in large numbers in units of Class A, Class B, and Class C addresses, so they were about to hit the bottom soon.

IP addresses are finite. The possibility of exhaustion of IP addresses has come to be feared.

But there is a problem.

This is because there is a rule that "the same address does not exist more than once" for IP addresses.

There are several methods that have been devised to deal with this IP address exhaustion problem.

IPv6 is one of them. Since IPv6 consists of 128 bits,

 2 128  = 3.4 × 10 38  pieces

 Only about 4.3 billion x about 4.3 billion x about 4.3 billion x about 4.3 billion IP addresses can be secured. This number is enough IP address space to not run out.

 However, there are various obstacles in moving to IPv6. This is because network lines, service programs, and network terminals must support IPv6.

*Since there is no urgency to migrate to IPv6 at the moment, it is difficult to say that it is being used.

private IP address

Private IP addresses were considered as a solution to the problem of IP address exhaustion.

 The idea is that if you set a special IP address that is used only for the local network and prevent it from flowing out to the Internet, you can use the IP address even if it overlaps.

The private IP address is as follows.

class A10.0.0.0 to
class B172.16.0.0 to
class C192.168.0.0 to

private IP address

By using this private IP address, you can freely build a LAN without applying for and obtaining an IP address.

 But with this private IP address, I can't connect to the internet. It's because it's a device on the internet and it's configured not to be routable.

 In order to connect to the Internet from a terminal assigned a private IP address, a mechanism is required to convert the private IP address to a global IP address.

This mechanism includes NAT and IP masquerade, and I will explain this mechanism later.