Ethernet frame format
The Ethernet frame length we often say starts from the Destination MAC Address in the figure and ends at the FCS. The standard Ethernet frame length range is \ ([64,1518] \) , except for the destination MAX address 6 bytes, the source MAC address 6 bytes, the Ethernet protocol 2 bytes, the check code 4 bytes, the payload payload The length range is $ [46,1500]. The maximum value of this payload is called MTU (Maximum Transmission Unit).
- EtherType : Ethernet protocol, the network card is used to distinguish what upper layer protocol is encapsulated, and then notify different protocol modules to take the data.
- Payload : The maximum length of the allowable load corresponds to the maximum transmission unit of the load.
- FCS : Frame Check Sequence, frame check code, and CRC is cyclic redundancy check algorithm, FCS can be generated by CRC algorithm, can also be generated by other algorithms.
Ethernet transmission reliability
In the tcp / ip protocol stack, in addition to the tcp protocol of the transport layer, the udp of the transport layer, and the network layer and data link layer below the transport layer are all "delivered as best as possible". Therefore, Ethernet transmission is not reliable.