Multicast between IP addresses and MAC addresses

The IP address and the MAC address are divided into three types: broadcast address, multicast address, and unicast address. First, FF: FF is undoubtedly a broadcast address. Each ENI is assigned a unique Unicast address when it leaves the factory. The first 24 bits are the ID of the equipment manufacturer, which is allocated by IEEE (Association of Electrical and Electronics Engineers, the last 24 bits are the unique ID specified by the device manufacturer for the NIC. For example, 08: 00: 20: 0A: 8C: 6D is the unicast address. 08:00:20 is the ID of the famous CPU vendor AMD. The Unicast address is characterized by a 0-bit forward of the first eight digits, so the unicast address has a total of 47-bit address spaces. Another type of address is the multicast address. MAC multicast addresses are characterized by 1 in the first eight bits, so the MAC multicast address space is quite large-except for the 47-bits of all 1. For example, 01: 80: C2: 00: 00 is a multicast address, indicating the 802.1d bridge multicast group. The bridge uses this address to exchange configuration information between each other, run the distributed spanning tree algorithm, and eliminate loops in the network topology. The IP layer also has the concepts of unicast, multicast, and broadcast. 01: 00: 5E: 00: 00: 00: 00: 00 to 01: 00: 5E: 7F: FF. A total of 23 digits correspond to IP multicast addresses. If an IP multicast address is given, the bitwise operation of its low 23 bits and 01: 00: 5E: 00: 00: 00 is taken as the bitwise operation, to a MAC multicast address. However, the IP multicast address has a 28-bit address space, but the corresponding MAC multicast address only has 23 digits. In this way, each 32 IP multicast addresses are mapped to the same MAC address. The MAC multicast address space is much larger than the IP multicast address space. If only the IP protocol is available at the network layer, IP multicast addresses can be mapped to MAC multicast addresses one to one! However, MAC address is a data link layer concept, and its upper-layer network layer is far from only IP addresses.