Basically any IP address with 40.35.1 or 168.35.1 as the last three octets carry the same multicast MAC address so you have potentially 32 addresses with the same multicast MAC address! So 192.168.35.1 has a multicast MAC address of 01-00-5E-28-23-01.Ĭan you spot an issue here? Hopefully you can. Our multicast MAC address is now 01-00-5E-28-23-01 In this example the value is 1 which equals 0x01. To calculate the value of ZZ take the fourth octet and convert it to hex. Our multicast MAC address is now 01-00-5E-28-23-ZZĤ. ![]() In this example the value is 35 which equals 0x23. To calculate the value of YY take the third octet and convert it to hex. Our multicast MAC address is now 01-00-5E-28-YY-ZZģ. In this example, the value of 168 is greater than 128 so we subtract 128 from 168 to give us a value of 40. If the value of the second octet is greater than 128 then subtract 128 from the second octet. To calculate the value of XX take the second octet. Start with a half-filled multicast MAC address of 01-00-5E-XX-YY-ZZĢ. Let us try and convert 192.168.35.1 to a multicast MAC addressġ. ![]() Therefore it must follow that a value of 6 in the second octet must be the same as 134 in the second octet as the high-order bit (i.e. If you think about this we are not using the high order bit in the second octet which carries a value of 128. ![]() To do this we need to convert the last 23 bits of the IP address in question. The first half of a multicast MAC address is 01-00-5E so we need to work out the second half. It's been a while but here's a quick post on how to calculate a multicast MAC address from an IP address.
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