What is the OUI field of the MAC address for IPv4 multicast addresses?

The Internet Assigned Numbers Authority (IANA) has allocated the Organizationally Unique Identifier (OUI) 01-00-5E for mapping IPv4 multicast addresses to Layer 2 Ethernet MAC addresses. When an IPv4 multicast packet is encapsulated in an Ethernet frame, the destination MAC address is constructed using this prefix. The first bit of the MAC address (01 hex) correctly identifies it as a multicast (group) address. The subsequent 23 bits of the MAC address are derived from the lower 23 bits of the Class D IPv4 multicast group address, resulting in a MAC address in the format 01-00-5E-xx-xx-xx.

A. 00-01-5e: The first octet 00 would incorrectly identify this as a unicast address, as the Individual/Group (I/G) bit is 0.

B. 00-01-5f: This is incorrect for the same reason as option A; the first octet 00 designates a unicast address, not multicast.

D. 01-00-5f: The standard OUI for IPv4 multicast uses 5E as the third octet, not 5F. This prefix is not assigned for this purpose.

1. IETF RFC 1112, "Host Extensions for IP Multicasting": Section 6.4, "IP Multicast-Address to Ethernet-Address Mapping", states, "An IP host group address is mapped to an Ethernet multicast address by placing the low-order 23 bits of the IP address into the low-order 23 bits of the Ethernet multicast address 01-00-5E-00-00-00."

2. Nokia SR OS R21 Multicast Protocols Guide (Part No. 3HE 17108 AAAD TQZZA): In the "IGMP" chapter, section "Layer 2 and Layer 3 Mapping", the guide describes this standard mapping: "The IANA owns an Ethernet MAC address block: 01:00:5e. This is the first 24 bits of the MAC address. This block of addresses is used for multicast applications."

3. Stanford University, CS144: Introduction to Computer Networking: Lecture slides on "Switching & Forwarding" detail the IP multicast to Ethernet MAC address mapping, explicitly showing the prefix as 01:00:5e. (e.g., Fall 2013, Lecture 6, Slide 25).