The same MAC address), you are going to be swamped with the download traffic as well as your You are subscribed to a streaming video feed on multicast IP address 237.129.2.3 (which maps to High-bandwidth software download is being transmitted on multicast IP address 224.1.2.3 and IP-aware and will do their multicast filtering based on MAC addresses. Similar) will not affect network performance for all users. Users will only "see" multicast traffic they haveĪctually asked for, so that (for example) a high-bandwidth software download (using Ghost or something This has implications for multicast application design. Rather,Įach multicast MAC address will be shared by 32 IP addresses. Not a one-to-one mapping between multicast IP address and multicast MAC addresses. Significant 9 bits of the multicast IP address are quite simply ignored and the remainingĢ3 bits are copied into the lowest 23 bits of the MAC address.Īs a consequence of this, 5 bits of "useful" IP address information being scrapped, there is Non-technical reasons which need not detain us here). Significant three bytes of the MAC address) available into which to encode the IP address.Īctually, it is even worse than this.only the lower 23 bits are available for use (for The astute reader may have noticed a problem by now: There are only 24 bits (the least If we ignore the four most significant bits of the multicast IP address (which,Īs noted earlier, will always be "1110"), that leaves 28 bits of IP address information which Traffic, we would ideally like a one-to-one mapping between multicast IP addresses and multicast Since it is obviously infeasible to have an equivalent of ARP when transmitting multicast If you aren't interested and reading this but just need to do a conversion you can skip ahead to the Address Converter Tool. For IP multicast specifically, the Ethernet prefix In the Ethernet world, a multicast MAC address is distinguished by a binary '1' in the least If you are looking for something to test IP multicast on your network you might like to check out our free (but very unfinished !) IP Multicast Tester Ethernet Addressing For the honours students, they are distinguished by the
World, they would have been called Class D addresses (although nowadays it is not considered polite
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