1.80 belongs to TCP port, which is a dedicated port for connecting to the Internet. If port 80 is occupied, you can't connect to the Internet, and UDP is for LAN. For example, two QQ users in the same LAN will use UDP protocol to transfer files.

2.80 is a local port, which means that if a local computer wants to connect to the Internet, it can only pass through port 80, and no other ports can.

3.2 1, 80 and other special ports are fixed and will not be repeated. Only some larger ports such as 8888 and 9999 will be used by some software, which is better than P2P, Donkey and tomcat.