This is the internal campus network of Renai College of Tianjin University. Inquiring about the website was made by Mr. Jiang from the Computer Department. E-mail query websites rely on TCP/IP protocol to realize the interconnection of different hardware structures, different operating systems and different network systems around the world. On the Internet, each node relies on a unique IP address to distinguish and contact each other. An IP address is a 32-bit binary address, which consists of four 8-bit fields, each separated by a dot to identify the TCP/IP host.

Each IP address contains two parts: network ID and host ID. The network ID identifies all hosts on the same physical network, and the host ID identifies each host on the physical network, so each computer on the whole Internet is identified by its own unique IP address. IP address forms the foundation of the whole Internet, which is so important that every computer connected to the Internet has no right to set its own IP address. There is a unified organization-iana, which is responsible for assigning a unique network ID to the organization that applies for it. An organization can assign a unique host ID to each host in its own network, just as a unit has no right to decide the street name and house number of its own city, but it can decide its own office number.