Gateways are also called gateways and protocol converters. Gateway is located at the transport layer to realize network interconnection. It is the most complex network interconnection equipment, and is only used for the interconnection of two networks with different advanced protocols. The structure of gateway is similar to that of router, but the difference is the interconnection layer. Gateway can be used for wide area network interconnection and local area network interconnection.

In network technology, ports have two meanings: one is physical ports, such as interfaces used by ADSL modems, hubs, switches and routers to connect other network devices, such as RJ-45 ports and SC ports. The second is logical port, which generally refers to the port in TCP/IP protocol. Port numbers range from 0 to 65535, such as port 80 for browsing web services, port 2 1 for FTP services and so on. What I want to introduce here is the logical port.

So what does the port in TCP/IP protocol mean? If the IP address is compared to a house, the port is the door of the house. A real house has only a few doors, but an IP address can have 65536 ports! Ports are marked by port numbers, which are only integers from 0 to 65535.

What's the use of ports? As we know, a host with an IP address can provide many services, such as Web services, FTP services, SMTP services and so on. These services can be completely realized through 1 IP address. So, how does the host distinguish different network services? Obviously, you can't just rely on ip addresses, because IP addresses and network services have a one-to-many relationship. In fact, different services are distinguished by "IP address+port number".

It should be noted that the ports are not in one-to-one correspondence. For example, when your computer accesses the WWW server as a client, the WWW server uses the "80" port to communicate with your computer, but your computer may use the "3457" port.