Understand the local area network and the IP allocation of the local area network in vernacular (effective guidance)

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scene preset

One day, you called Telecom and said that you want to apply for broadband, and soon the Telecom service pulled the network cable to your home, and then you got a key to the world's gate (public network)-network At this time, you follow the instructions to plug in the router, the
router The moment you plug in the host computer and turn it on and connect to the Internet, you will have the unique public IP address in the world assigned to you by the telecommunications service. My friends are all in the computer industry, and you know very well: if you don't turn off the router, the address will be fixed, and if you turn it on again, it will randomly assign an ip to you.
Because:

1. The ip address cannot be used by two computers at the same time (that is, the moment you shut down, the ip address is recycled, it may be assigned by other friends who have just surfed the Internet, and the same ip address cannot be assigned when you turn on the computer again),
2. Moreover, IP resources are insufficient, so dynamic acquisition can effectively solve such resource problems
3. If the need for a permanently fixed ip address is either to tamper with the router to make it work permanently, or to spend a lot of money to apply for a dedicated line (Telecom, China Mobile, China Unicom), then it can be easily solved.
   But why do you say tampering with the router? Because the home broadband is pppoe dial-up Internet access, each dial-up will assign an ip address to the device. That is, if you want to surf the Internet, you have to dial up to obtain an IP address. Then you can get a "permanent ip" by dialing once and surfing the Internet all the time. Of course, if the network cable is directly connected to the computer host