3Com corebuilder 3500 Implementation Manual page 340

340 C 13: IP M R
HAPTER ULTICAST OUTING
Reserved MAC Addresses
IANA also controls a reserved portion of the IEEE-802 MAC-layer
multicast address space. All addresses in this block use hexadecimal
format and begin with 01-00-5E. A simple procedure maps Class D
addresses to this block, so that IP multicasting can take advantage of the
hardware-level multicasting supported by network interface cards (NICs).
The mapping process involves placing the low-order 23 bits of the Class D
address (binary format) into the low-order 23 bits of the MAC address
(hexadecimal format). For example, the Layer 3 address 224.10.8.5 maps
to the Layer 2 MAC address 01-00-5E-0A-08-05.
To send a multicast packet, a source station inserts the Class D address in
the IP packet, the network interface card maps that address to a IEEE-802
Ethernet multicast MAC address, and sends the frame. A host that wants
to receive packets that are addressed to this group notifies its IP layer as
such.