What is the relationship between gateways, bridges, routes, protocols, dns, switches and servers in Hong Kong?

Server: a machine that provides services for you. It is equivalent to various storefronts on the roadside. Although theoretically any family can open a shop to provide services for you, it is not suitable for opening a shop due to the limitation of various hardware resources. For example, the roads in the community are relatively narrow (the broadband bandwidth is relatively narrow), the place at home is too small, the equipment is too few (the hardware performance is not good enough to provide services for a large number of customers), the address in the community is difficult to find (there is no external IP, in fact, if the server is located in the intranet, it is basically impossible to find it from the external network), and it is not convenient to ask for directions without a signboard (there is no domain name application).

DNS: Domain name system, equivalent to a huge database, translates store names (domain names) into addresses (IP addresses).

Switch: At the crossroads, you can go either way.

Router: I am a road idiot. If you don't know the way out of the community, ask for directions. Routers can help you solve the problem of asking for directions in LAN. Routers divide networks into two parts: internal networks and external networks. Equivalent to the door of the community. Of course, it can also be used as a switch when the door is closed (the WAN port is not wired), and an inquiry barrier (firewall) can also be set up.

Gateway: Who are so many people asking for directions? Of course, it is the community doorman (router), but where is the doorman? It has an address and must be set in advance. The gateway must be in the local area network. Out of the neighborhood, I went crazy. You asked me to go to xx Road and ask Uncle xx. I can't find it. At the same time, the gateway must have a connection with the external network, so that it can be queried.

Etiquette: Asking for directions requires others' understanding, and asking for services also requires making requests. A protocol is an agreed language. For example, HTTP protocol: give me the name of the webpage: blahblah, and reply: 200 OK blahblah.

Bridge: There is only one aisle in the community. When there are many people, it will be crowded and there is no way to expand. So a new community was built behind, connected with the original community by a bridge and managed in a unified way.

VPN: Shuttle bus from home to company. How to get to the company from home? You don't need to know that VPN will help you. So you can visit the company's intranet at home at any time, or you can get off at the back of the company and go out from the company's gate (gateway) to visit the outside address. (You can hide in the car to avoid the interrogation on the road)

IPV6: There are too many people in China. Let's emigrate. Therefore, a longer address is needed.

IPV6/IPV4 tunnel: China people don't know the English address, so it's no use knowing it. They can only pretend to go to the airport first and ask: Where is the airport? Then everyone understood. Then when we arrive at the airport, we ask how to get to XXX address with English address. The process of asking for directions from a home with a Chinese address to the airport is a tunnel. Only when you get off at the other end of the tunnel can you ask for directions with your real address.

Host name not found: DNS error, domain name can not find the corresponding IP address, the reasons may be as follows:

1. The domain name is misspelled.

2. The 2.DNS server is unreliable or intentionally conceals the truth.

There was a robbery on the road, and you changed your address with a note with an address returned by DNS (DNS hijacking).

Solution: If there is a problem with the DNS server, there is only one solution. Change DNS address. If it is DNS hijacking, you can only get the IP address from other channels and record it in /etc/hosts.