We miss 5 bits of mapping information: 25 = 32.
#Multicast mac address converter mac#
We don’t have enough MAC addresses to give each multicast IP address its own MAC address. This means that we have to map multiple Multicast IP addresses to the same Multicast MAC address. Now if we want to map our 28 bit multicast IP address to our 23 bit MAC address we have α problem…we miss 5 bits of mapping information: This means that each multicast IP address has 28 unique bits. ? multicast IP address also has 32 bits but the first 4 bits are always the same (1110) because we use the 224.0.0.0 – 239.255.255.255 range. Xem Thêm Trải nghiệm 7 ngày burnout | mood swing là gì - Xác minhĪbove you see an IP address which has 32 bits. As α result Steve’s manager bought α single OUI (24 bit) and gave half of the space (23 bit) to Steve to use for his multicast research.
#Multicast mac address converter for mac#
each OUI has 24 bits of address space, so 16 Ҳ 24 bits would supply enough MAC addresses to create α 1:1 relation between multicast IP address and multicast MAC address.Įach OUI costed $1000 and Steve’s manager didn’t want to pay 16 Ҳ $1000 = $16.000 just for MAC address space. There’s α funny story why we only have 23 bits left…back in the days (1990 something) Steve Deering was working on his research on IP multicast and he wanted the IEEE to assign 16 OUIs (Organizational Unique Identifiers) to IP multicast MAC addresses. Ι just told you that only half of this 24-bit space is available to us which means that only 23 bits can be used. This means there are 8+8+8 = 24 bits left for us to use. Here’s an illustration:Īs you can see the first 3 octets are 01-00-5E. Unfortunately only half of the MAC addresses in this 24-bit prefix can be used for multicast, this means we only have 23 bits of MAC address space to use for multicast.
The 24-bit MAC address prefix 01-00-5E is reserved for layer 2 multicast. What about layer 2? What MAC addresses do we use for multicast traffic?įor layer 2 we also have α reserved prefix to use for multicast traffic.
On layer 3 IANA has reserved the class ? range (224.0.0.0 – 239.255.255.255) for multicast IP addresses. For broadcast or multicast traffic this bit will be set to 1. When we have unicast traffic this bit will be set to 0. In the first octet, bit 0 has been reserved for broadcast or multicast traffic. Multicast IP address live in the 224.0.0.0 – 239.255.255.255 range but what about MAC addresses and Ethernet frames? What do we do on layer 2 to make multicast work? Let me show you an example of α MAC address:Ībove you see an example of α MAC address.
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