What is the structure of physical address

#The actual address corresponding to the storage unit in the network card physical address memory is called the physical address, which corresponds to the logical address. The physical address of the network card is usually written into the network card's EPROM (a flash memory chip that can usually be erased by a program) written by the network card manufacturer. It stores the computer that actually identifies the computer that sends the data and receives the data when transmitting data. The address of the host.

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## »The address in the network is divided into physical addresses and logic addresses. Two Class , compared with the IP address of the network layer, the port number of the transport layer and the user name of the application layer, The MAC layer address of the LAN is processed by hardware and is called a physical address or hardware address.

The port number of the IP address transport layer and the user name of the application layer are logical addresses that are processed by software.

MAC address is also called physical address. Most LANs identify a networked computer or other device by assigning a hardware address to the network card.

The so-called physical address refers to the address solidified in the EPROM of the network card. This address should be guaranteed to be unique in the entire network. The IEEE Registration Committee assigns the first three bytes of the physical address to each manufacturer, which is the company identification.

The last three bytes are allocated by the manufacturer. The number of network cards a manufacturer can produce by obtaining an address of the first three bytes is 16,777,216. A network card corresponds to a physical address. In other words, the first three bytes corresponding to the physical address can be used to know its manufacturer.

For example, the address fixed in the network card is 002514895423, then this network card is inserted into host A, and the physical address of host A is 002514895423, regardless of whether host A is connected to LAN 1 or LAN 2, or No matter where this computer is moved, the physical address of host A is 002514895423. It is immutable and will not be the same as any other computer in the world.

When host A sends a frame, when the network card executes the sending program, it directly writes this address as the source address into the frame. When host A receives a frame, it directly compares this address with the destination address of the received frame to decide whether to receive it.

The physical address is generally recorded as 00-25-14-89-54-23 (the address of host A is 002514895423).

In other words, during the physical transmission process at the bottom of the network, the host is identified by its physical address, which is generally unique in the world.

For example, the physical address size of the famous Ethernet card is 48 bits, the first 24 bits are the manufacturer number, and the last 24 bits are the network card number, such as: 44-45-53-54-00- 00, stored in the host interface in a machine-readable manner.

The Ethernet Address Management Institute (IEEE) divides Ethernet addresses, that is, different combinations of 48 bits, into a number of independent consecutive address groups. Manufacturers of Ethernet network cards purchase one of the groups, and the specific production , assign unique addresses to the Ethernet cards one by one.

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