Multicast IP Addresses and MAC addresses


224.0.0.0      =    01-00-5E-00-00-00


224.0.0.5      =    01-00-5E-00-00-05


239.255.0.6    =    01:00:5e:7f:00:06

239.11111111.0.6

01:00:5e:0xxxxxxx:00:06

01:00:5e:01111111:00:06

0111  1111
7     f

01:00:5e:7f:00:06


•224.1.1.1
•224.129.1.1
•225.1.1.1
•…
•…
•…
•238.1.1.1
•238.129.1.1
•239.1.1.1


01-00-5E-01-01-01


http://nettools.aqwnet.com/ipmaccalc/

http://www.cisco.com/c/en/us/td/docs/ios/solutions_docs/ip_multicast/White_papers/mcst_ovr.html


Why just 23 Bits?

There’s an interesting story as to why only 23 bits 
worth of MAC address space was allocated for IP multicast. 

Back in the early 1990s, Steve Deering was bringing some of his
research work on IP multicasting to fruition, 
and he wanted the IEEE to assign 16 consecutive 
Organizational Unique Identifiers (OUIs) for use as 
IP multicast MAC addresses. 

Because one OUI contains 24 bits worth of address space, 
16 consecutive OUI’s would supply a full 28 bits worth of 
MAC address space and would permit a one-to-one
mapping of Layer 3 IP multicast addresses to MAC addresses. 

Unfortunately, the going price for an OUI at the time was $1000 
and Steve’s manager, the late Jon Postel, was unable
to justify the $16,000 necessary to purchase the full 28 bits 
worth of MAC addresses.

Instead, Jon was willing to spend $1000 to purchase one OUI 
out of his budget and give half of the addresses 
(23 bits worth) to Steve for use in his IP multicast research.


Ali Aydemir 2010