Analysis of computer network protocol headers-Ethernet

Brief Analysis of the network protocol header-Ethernet [Ethernet protocol frame structure] when it comes to the Ethernet frame structure, its historical evolution is slightly chaotic. We will introduce the evolution of Ethernet standards. In 1980, DEC, schile, and Intel jointly developed the Ethernet I standard, defining the Ethernet frame format for the first time. On 1982, www.2cto.com updated the first version of www.2cto.com, which mainly changed the physical interface and the frame format remained unchanged. This updated version is named Ethernet II standard. At the same time, IEEE began to focus on the development of Ethernet standards, and plans to introduce the Ethernet 802.3 international standard. Three years later, in, IEEE officially introduced the IEEE Standard Specification. Since then, Ethernet has an authoritative international standard, the main difference between this version and the Ethernet II standard is that it replaces the original protocol type field with the frame length field and adds the 802.2 LLC header to identify the upper-layer protocol. The resulting 802.3/802.2 SNAP is the Ethernet standard released by IEEE to better support the IP protocol. Compared with the 802.3 standard, it extends the LLC header and adds a 2-byte protocol type domain. Www.2cto.com at present, we are most often using the Ethernet II standard released in 1982. Therefore, I listed the Ethernet II standard frame format here:
The Type field is 2 bytes to identify the protocol type used by the previous layer, such as IP protocol (0 × 0800. Data field. The length range is 46 to 1500. Why? Because the minimum specification for an Ethernet package is 64 bytes, if not, it will be filled with 64 bytes. The other parts of the Ethernet frame format are 6 + 6 + 2 + 4 = 18 bytes, so the minimum length of the Data part is 64-18 = 46 bytes; the maximum length of the Ethernet package is 1518 bytes, so 1518-18 = 1500 bytes. The final FCS field is the Frame Check Sequence field, which is used to save the CRC Check value.

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