Multicast IP Address to MAC address mapping

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Hi James,

I understand that these calculations make your head spin…they are kinda annoying :slight_smile:

Here’s how to figure out what MAC address your IP address maps to:

  1. We convert your IP address to binary:

decimal: 239.192.0.1
binary: 11101111 11000000 00000000 00000001

  1. We only care about the last 23 bits of your IP address so I removed the first 9 bits, that gives us:

1000000 00000000 00000001

  1. Now we need to convert these 23 bits into hexadecimal. You need to take 4 binary bits and convert them to hexadecimal:

binary: 100 0000 0000 0000 0000 0001
hex: 4 0 0 0 0 1

That gives us:

40:00:01

The first part of a multicast MAC address always starts with 01:00:5e so let’s put that in front:

01:00:5e + 40:00:01 = 01:00:5e:40:00:01 (your multicast MAC address).

Does that help?

Rene

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