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ISCOM2600G-HI (A) Series Configuration Guide
Figure 8-2 Basic concepts in multicast
Multicast address
To make multicast source and multicast group members communicate across the Internet, you
need to provide network layer multicast address and link layer multicast address, namely, the
IP multicast address and multicast MAC address.
Internet Assigned Numbers Authority (IANA) assigns Class D address space to IPv4 multicast;
the IPv4 multicast address ranges from 224.0.0.0 to 239.255.255.255.
When the Ethernet transmits unicast IP packets, it uses the MAC address of the receiver as the
destination MAC address. However, when multicast packets are transmitted, the destination is
no longer a specific receiver, but a group with an uncertain number of members, so the
Ethernet needs to use the multicast MAC address.
The multicast MAC address identifies receivers of the same multicast group on the link layer.
According to IANA, high bit 24 of the multicast MAC address are 0x01005E, bit 25 is fixed
to 0, and the low bit 23 corresponds to low bit 23 of the IPv4 multicast address.
Figure 8-3 shows mapping between the IPv4 multicast address and MAC address.
IP multicast address
Multicast MAC address
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