From: Joel W. Ekis (jekis@xxxxxxxxx)
Date: Mon Mar 20 2000 - 12:01:46 GMT-3
Depends, how good are you at yoga?
At 06:16 AM 3/20/2000 -0800, jpritcha@csc.com wrote:
>
>
>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 ma
ke
>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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