MAC Address (unicast, multicast, broadcast address classification)

Brief introduction

Before a manufacturer can manufacture a network card, it must register with the IEEE to obtain a vendor code length of 24bit, also known as OUI (Organizationally-unique Identifier). In the process of manufacturing the network card, the manufacturer will burn a 48bit bia (burned-in address, Cure addresses) address to each of the NIC's ROM, the first 3 bytes of the BIA address are the manufacturer's OUI, and the last 3 bytes are determined by the manufacturer itself, but different network cards, The following 3 bytes of its BIA address are not the same. The BIA address that is burned into the network card cannot be changed and can only be read and used. As shown in the format of the address.

Note that the BIA address is just one of the MAC addresses, and more accurately, the BIA address is a unicast MAC address. MAC addresses are divided into 3 types, namely unicast MAC address, multicast MAC address, broadcast MAC address. The 3 types of MAC addresses are defined as follows:

1) unicast MAC address refers to the MAC address where the lowest bit of the first byte is 0.
2) The multicast MAC address refers to the MAC address where the lowest bit of the first byte is 1.
3) The broadcast MAC address refers to the MAC address where each bit is 1. Broadcast MAC address is a special case of multicast MAC address.

A unicast MAC address (such as a BIA address) identifies a specific NIC, a multicast MAC address identifies a set of network cards, and a broadcast MAC address is a special case of a multicast MAC address that identifies all network cards. From what we can find, not the first 3 bytes of a MAC address are OUI, only the first 3 bytes of the unicast MAC address are OUI, and the first 3 bytes of the multicast or broadcast MAC address must not be OUI. It is important to note that the lowest bit of the first byte of the OUI must be 0.

MAC Address Example

MAC Address (unicast, multicast, broadcast address classification)