From: jpritcha@xxxxxxx
Date: Mon Mar 20 2000 - 11:16:36 GMT-3
Joel,
I don't mind looking silly. Actually I've become quite good at it. Thanks to
your 'trick' I know I will never mess up this conversion again.
Can I use any of my body parts to help me with route redistribution?
Thanks again,
Jim
jekis@cisco.com on 03/20/2000 05:36:31
Please respond to jekis@cisco.com
To: ccielab@groupstudy.com
cc: (bcc: James F Pritchard/TMG/CSC)
Subject: Re: Canonical stuff...
If you don't mind looking a bit silly, you can do this with your hands...
Hold both hands in front of you. Fingers up, thumbs tucked into your palm.
Have your palms facing towards you. Each finger represents a bit. Extend a
finger upward for each '1' and fold it down for each '0'. Apologies to the
arthritic and those offended by obscene gestures.
You now have represented the byte with your hands.
To convert, rotate your palms away from you and then cross your forearms to mak
e
an 'X'. Read your fingers to reconstruct the HEX representation. Works going
from canonical to non-canonical and vice versa.
Joel
At 04:53 PM 3/16/2000 -0500, Scott Morris wrote:
>Hopefully this will all make sense out of context. I happened to write a
>segment of a Token Ring chapter that dealt with canonical conversion steps.
>This doesn't mention any areas that NEED or DON'T NEED the canonical
>addresses, but it will explain the steps to convert the addresses so things
>make sense to you!
>If you have any questions, or my lack of context doesn't make sense, feel
>free to let me know!
>
>----------------------------------------------------
>The first thing we will do is look at the MAC address in pair-bytes, which
>is the way that most people are used to seeing the MAC address represented
>anyway. So our Token Ring interface is now looking like 00-00-30-A9-60-16.
>
>The next step is to convert each pair-byte into binary. Remember that the
>MAC address is a hexadecimal number, so each digit/character represents 4
>bits of information. For a refresher-course, you can look back to Section
>1.11 for information on numbering schemas and converting between them.
>
>4 bits in binary will give the following positions for our first pair ?00?:
>
>0 0 0 0 0 0 0 0
>8 4 2 1 8 4 2 1
>23 22 21 20 23 22 21 20
>
>
>It?s really simple when the numbers are 0!!! So let?s skip to the ?30?
>group:
>
>0 0 1 1 0 0 0 0
>8 4 2 1 8 4 2 1
>23 22 21 20 23 22 21 20
>
>In binary, the ?30? is 00110000.
>
>Now, we are going to perform the bit-swapping part! No magic is involved,
>so quit conjuring up images of David Copperfield and sounds of a drum roll!
>
>As we stated, this process takes place within each pair of hexadecimal
>characters (which, since each is 4 bits, 4 bits + 4 bits = 8 bits = 1 byte
>of information!). So we?ll look at the ?30? pair first. We are going to
>flop the entire group, where the right-most bit will become the left-most
>bit.
>
>If we look at the number above, 00110000 will become 00001100. So let?s
>plug it back in to the 4-bit matrix we?ve created:
>
>0 0 0 0 1 1 0 0
>8 4 2 1 8 4 2 1
>23 22 21 20 23 22 21 20
>
>We now get a 0 and a C in hexadecimal. So the ?30? pair will become ?0C?!
>
>So let?s look at each pair now! Remember the original address was
>00-00-30-A9-60-16!
>
>?00? is 0000 0000 in binary. Interestingly enough, when you reverse it all,
>it looks the same! So we get by really easy for the first two pairs!
>
>?30? is 0011 0000 in binary. Swapped, it becomes 0000 1100 as discussed
>above. That is ?0C? in hexadecimal.
>
>?A9? is 1010 1001 in binary. Swapped, it becomes 1001 0101, which is ?95?
>when converted back to hexadecimal.
>
>?60? is 0110 0000 in binary. Swapped, it becomes 0000 0110, which is ?06?
>in hexadecimal.
>
>?16? is 0001 0110 in binary. Swapped, it becomes 0110 1000, which is ?68?
>in hexadecimal.
>
>So when we put each concatenated pair back together, we find that the Token
>Ring address has become 00-00-0C-95-06-68. That number-sequence is what we
>will see contained within a Destination Address or Source Address portion of
>a Token Ring frame.
>
>
>Scott Morris, MCSE, CNE(3.x), CCDP (R&S), CCIE (R&S) #4713, Security
>Specialization, CCNA - WAN Switching
>smorris@ccci.com
>----------------------------------------------------------------------------
>------------------------------
>Chesapeake Network Solutions http://www.ccci.com
>Cell Phone: 941-350-8590 e-mail:smorris@ccci.com
>Pager: 800-490-1326 Fax: 606-225-8403
>
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