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Forum Replies

  1. This is killing me. I have a task to convert to a mac-address. I am just not getting it right now.

    01:00:5e:ef: is as far as I get…how to I convert the 100 (binary for 192 is 11000000 so I eliminate the first 1) to hex? 01:00:5e:ef:?0:00:01 is where I am at.

  2. 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:

    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

    ... Continue reading in our forum

  3. Hi Rene,

    Excellent post and excellent explanation of what should be simpler and was made unnecessarily complex :slight_smile:

    Just one small correction:

    Where you say “The multicast IP addresses above all map to the same multicast MAC address (01-00-5E-01-01)”, I think you’re missing one octet. I believe it should be 01-00-5E-01-01-01.

  4. Hi Rene,

    Excellent creation as usual . Please confirm my understanding is correct which is grabbed from this lesson. Please let me know if I am wrong :slight_smile:

    General format of MAC address is MM:MM:MM:SS:SS:SS.The leftmost 6 digits (24 bits : MM:MM:MM ) called a “prefix” is associated with the adapter manufacturer.
    The rightmost digits (24 bits : SS:SS:SS) of a MAC address represent an identification number for the specific device with the same vendor prefix.

    But here in this multicast we use the leftmost 3 octets are (24 bits : MM:MM:MM) always 01-00-5E and the right

    ... Continue reading in our forum

  5. In terms of Layer 2 multicast addresses, it seems there are some exceptions to the 0100.5e.X prefix rule?

    0100.0ccc.cccd is for PVST and is considered multicast
    0180.c200.0000 is for regular spanning tree and considered multicast

    I suppose these will never map to Layer 3 addresses so that’s probably why they appear random.

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