IPv4 multicast MAC Addresses

The MAC addresses used for IPv4 multicast (IPv4 multicast MAC addresses) have 01:00:5e prefix. IPv4 multicast MAC addresses are used as layer 2 (datalink layer) addresses for multicast type of network traffic. In multicast type of network traffic, a packet sent from a source is replicated as needed in the network to reach only to the end-users interested in that traffic. Users who are not interested in that traffic will not receive the copy of the packet. Multicasting is "one-to-many" type of network communication

I strongly suggest you to visit and learn below lessons before reading further about IPv4 multicast MAC Addresses.

The Ethernet MAC Address Range used for IPv4 multicast traffic is from 01:00:5e:00:00:00 to 01:00:5e:7f:ff:ff.

Refer following image, which shows the general structure of a multicast MAC address. As you can see from below image, the right-most bit in the first octet (the least-significant bit in the most-significant octet) of a multicast MAC address has been reserved as binary "1".


Please refer below image. As you can see from below image, left-most 24 bits of an IPv4 multicast MAC addresses are reserved as "01:00:5e". The next bit (25th bit) is reserved as "0". The remaining 23 bits (rightmost 23 bits) of IPv4 multicast MAC addresses are mapped to the rightmost 23 bits of a multicast IPv4 addresses (Class D IPv4 addresses).


From above image, you can see that all IPv4 multicast MAC addresses have a prefix of "01:00:5e". Any MAC address starting with "01:00:5e" is IPv4 multicast MAC address.

We have already learned that IP addresses are used in layer 3 (network layer) of TCP/IP protocol stack. MAC addresses are the addresses used in layer 2 (datalink layer) of TCP/IP protocol stack. In Ethernet LAN environments, as the packet moves down the TCP/IP protocol stack from layer 3 (network layer) to layer 2 (datalink layer) at the sending computer, if the destination IPv4 address is a Class D multicast IPv4 address the IPv4 datagram packet will be encapsulated with an Ethernet frame with IPv4 multicast MAC address (with a prefix of 01:00:5e) as the destination MAC address.

Please refer below wireshark packet caputure screenshot. You can see that when the destination IPv4 address is Class D multicast address, destination MAC address starts with "00:01:5e".


Related Tutorials
Unicast, Multicast and Broadcast
Broadcast domain
Binary Decimal and Hexadecimal numbers and conversions
How to use calculator for binary, decimal and hexadecimal number conversions
TCP/IP model
Datalink layer of TCP/IP model
Ethernet Frame Format
MAC addresses
Broadcast MAC Address - ff:ff:ff:ff:ff:ff
IPv4 multicast MAC Addresses
Network layer of TCP/IP model
IPv4 Protocol, IPv4 header and fields of IPv4 header
IPv4 addresses
Class A networks and Class A IP addresses
Class B networks and Class B IP addresses
Class C networks and Class C IP addresses
Class D multicast IP addresses
IPv4 link-local multicast addresses
IPv4 Internetwork control block multicast addresses
IPv4 Source-Specific Multicast (SSM) address reservation
IPv4 GLOP multicast addresses
Administratively scoped multicast address block or Limited scope addresses
Multicast IPv4 address to MAC address mapping
What is limited broadcast in IPv4 and how limited broadcast works
What is directed broadcast in IPv4 and how directed broadcast works
Transport layer of TCP/IP model
TCP/IP Encapsulation and Decapsulation
What is multicast
What is multicast group
Advantages and disadvantages of multicast
Comparison of multicast with unicast and broadcast
Advantages and disadvantages of multicast
How IPv4 multicast works on LAN