TCP/Socket learning --- Ethernet (RFC 894) frame format

TCP/Socket learning --- Ethernet (RFC 894) frame format where the source address and destination address are the hardware address (also called MAC address) of the network card, and the length is 48 bits, it is fixed at the factory of the NIC. Run the ifconfig command to check that the "HWaddr 00: 15: F2: 14: 9E: 3F" part is the hardware address. The protocol field has three values, corresponding to IP, ARP, and RARP respectively. The end of the frame is a CRC check code. The Data Length in an Ethernet frame is defined as a minimum of 46 bytes, a maximum of 1500 bytes, and a minimum of 46 bytes for ARP and RARP packets. Fill in the following bits. The maximum value of 1500 is the maximum transmission unit (MTU) over Ethernet. Different network types have different MTU. If a data packet is routed from the Ethernet to the dial-up link, if the packet length is greater than the MTU of the dialing link, fragmentation is required for the packet ). The output of the ifconfig command also contains "MTU: 1500 ". Note that the MTU concept refers to the maximum length of the payload in a data frame, excluding the length of the frame header.