MAC address

　The Mac (Media/Medium Access Control) address is a unique identification number given to devices connected to the network.Specifically, it is given to PCs and servers, virtual machines NIC (Network Interface Card), routers and LAN switch interfaces.In the LAN consisting of Ethernet, the data is stored in a "frame" and transmitted and received.Specify the source and destination of this frame by the MAC address.

　The LAN switch to transfer the frame records all the MAC addresses of all terminals connected to the tip of each port.See this to send the corresponding frame from the appropriate port.In this way, the frame is delivered to the target equipment.If there is no MAC address that corresponds to the table, the LAN switch will send the frame on a broadcast.

　The NIC MAC address mounted on the terminal can be confirmed by the command.We use "IPCONFIG" on Windows, and "IP" for Linux.

NICの製造元が分かる

　The length of the MAC address is 48 bits.It is generally written in a hexadecimal number separated by hyphen or colon every 8 bits, such as "00-01-02-AA-BB-CC" or "00: 01: 02: aa: bb: CC".。The MAC address assigned to each NIC must be unique.In other words, there are no NICs with the same MAC address in the world.For this reason, the manufacturers of network devices strictly manage the MAC address.

　MACアドレスの前半24ビットをOUI（Organizationally Unique Identifier）と呼ぶ。NICの製造元を表す識別子である（PICT1）。

　When examining the manufacturer from OUI, IEEE site (https: // RegAuth.Standards.IEEE.org/Standards-ra-web/pub/view.You can search by html#Registries).The manufacturer allocates the 24 -bit of the latter half of the MAC address.

　OUI helps to solve trouble.For example, if the behavior of a router or computer is strange, if the MAC address is divided, the device that is caused can be narrowed down.Effective for separation of disability locations.

　MAC addresses can also be used for terminal access control and authentication.For example, check the MAC address to identify the terminal and decide whether to allow access or block.This function is called a MAC address filtering and is equipped with many network devices.

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