What is an IP packet?

Packet is a data unit in TCP/IP communication transmission ". Some people say, isn't the frame transmitted in the lan? Yes, but the TCP/IP protocol works on the layer 3 (Network Layer) and Layer 4 (Transport Layer) of the OSI model, while the frame works on the Layer 2 (data link layer ). The content of the previous layer is transmitted by the content of the next layer. Therefore, in the LAN, "packets" are contained in "frames. The OSI (Open System Interconnection) model is a standard defined by the International Organization for Standardization (ISO). It defines a hierarchical architecture, each layer defines protocols for different communication levels. The OSI model has 7 layers and 17 layers: physical layer, data link layer, network layer, transmission layer, Session Layer, presentation layer, and application layer. The OSI model is logically divided into two parts: the 14 layers at the lower layer focus on the transmission of raw data, and the 57 layers at the higher layer focus on applications on the network. We can describe the concept of data packets using an image example: When we mail a product at the post office, although the product itself has its own packaging box, however, it is obviously impossible to pack only the original packaging box of the product during mailing. The packaging box of the built-in product must be placed in a specialized carton designated by the post office to mail the product. Here, the product packing box is equivalent to a data packet, and the product inside is equivalent to available data, while the dedicated carton is equivalent to a frame, and there is only one data packet in one frame. The "package" sounds very abstract. Is it invisible? Some technical means can be used to perceive the existence of data packets. For example, in Windows 2000 Server, move the mouse over the NIC icon in the lower-right corner of the taskbar (the NIC needs to be connected to a twisted pair and connected to the network), you can see "Send: ×× packet, receive: ** package "prompt. Data packet capture software can also capture and analyze data packets. It is the interface diagram of the data packet captured by the data packet capture software Iris. Here, you can clearly see the MAC address, IP address, protocol type port number, and other details of the captured data packet. By analyzing the data, the network administrator can know what kind of data packets are active in the network. Note: The structure of the data packet is very complex. It is not clear in just a few words. Here we will focus on the key components of the data packet, this is very important for understanding the Communication Principles of TCP/IP. A data packet consists of "Destination IP address", "source IP address", and "net data. The structure of the data packet is very similar to what we usually write. The destination IP address is the recipient's address, and the source IP address is the source of the data packet, it is equivalent to the sender's address, while the net data is equivalent to the content of the letter. It is precisely because data packets have such a structure that computers with TCP/IP protocols can communicate with each other. When we use a network based on the TCP/IP protocol, packets are actually transmitted in the network. Understanding data packets is of vital significance for network security in network management.