Neil, see if this helps...
Canonical / non-Canonical, LSB / MSB address format.
The physical bitstream always, independent from the topology,
starts with the I/G-bit ("group"-bit).
The destination address of a SRF-frame, for example
1000 0000 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001
is displayed in MSB-/ non-canonical format as
80 01 23 45 67 89
and in LSB- / canonical format as
01 80 C8 A2 E6 91
The source and the destination addresses are usually displayed by
FDDI and Ethernet in LSB-/canonical format, by Token-Ring in
MSB-/non-canonical format.
A typical MAC-address of a SK Concentrator II (FDDI), for example
00 00 5A 4F 01 89 (LSB / canonical)
is in MSB / non-canonical
00 00 5A F2 80 91
and is physically transmitted like this:
0000 0000 0000 0000 0101 1010 1111 0010 1000 0000 1001 0001
|
first Bit at the cable
The various topologies handle this as shown in the table:
| Ethernet | FDDI | Token Ring
--------------------------------------------------------------
phys. transmission | canonical | non-canonical | non-canonical
protocol Layer | canonical | canonical | non-canonical
Attention: the MAC-address you can see on Ethernet and FDDI
is normally LSB-/canonical format.
The MAC-address you can see on Token-Ring is
normally MSB-/non-canonical format.
How to convert from canonical to non-canonical format?
Trick: Read the single bytes bitwise from right to left.
Example 1
change this (which is LSB- / canonical)
00 00 5A 41 1E C4
in Bits:
0000 0000 0000 0000 0101 1010 0100 0001 0001 1110 1100 0100
to (in Bits):
0000 0000 0000 0000 0101 1010 1000 0010 0111 1000 0010 0011
Hex (which is MSB- / non-canonical)
00 00 5A 82 78 23
Example 2
change this (which is LSB- / canonical)
00 00 EF 03 16 20
in Bits:
0000 0000 0000 0000 1110 1111 0000 0011 0001 0110 0010 0000
to (in Bits):
0000 0000 0000 0000 1111 0111 1100 0000 0110 1000 0000 0100
Hex (which is MSB- / non-canonical)
00 00 F7 C0 68 04
regards,
mohan
-----Original Message-----
From: Maness, Drew [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, August 16, 2000 8:59 AM
To: [EMAIL PROTECTED]
Subject: RE: canonical and non-canonical addresses
Neil,
I'm not sure what your question is. The bits on the wire are transmitted
the same 01000000. Token-ring reads them one way (non-canonical) 01000000,
and Ethernet reads them another way (canonical)00000010. It is how the
network interface cards (NIC)/device drivers read the 0s and 1s that is
different.
I would be happy to help(since I have struggled with this myself) if you can
clarify your question
Regards,
Drew R. Maness, CCNP, CCDA, CCSI, MCSE
-----Original Message-----
From: Neil Desai [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, August 15, 2000 12:47 PM
To: [EMAIL PROTECTED]
Subject: Re: canonical and non-canonical addresses
Does any body know the answer to this one? Now I am getting a bit
frustrated. I have posted to this group only a couple of times and I never
get an answer. All I get is people asking me to look at the archives. I did
as much homework as possible before asking the group.
""Neil Desai"" <[EMAIL PROTECTED]> wrote in message
8n9llp$83c$[EMAIL PROTECTED]">news:8n9llp$83c$[EMAIL PROTECTED]...
> I am having a problem understanding the issues between canonical and
> non-canonical addressing. I understand that the bits are flipped within
the
> byte. On page 32-33 of Interconnections Second Edition she gives the
example
> of the address a2-41-42-59-31-51.
> Canonical:
> 10100010 01000001 01000010 01011001 00110001 01010001
> Non-Canonical:
> 01000101 10000010 01000010 10011010 10001100 10001010
>
> If you look at this you can clearly see that the address in canonical
format
> is not a group address (last bit of first byte is zero) but in
non-canonical
> format it is a group address. At this point I can see a big problem
because
> she also states:
>
> ".the group bit in addresses was defined not as "the most significant
bit"
> or the "least significant bit" but rather as "the first bit on the wire."
> Thus, an address that was a group address on 802.3 would not necessarily
> look like a group address when transmitted on 802.5 because a different
bit
> would be transmitted first."
>
> Here is the confusion: In canonical format the least significant bit is
> transmitted first and in non-canonical format the most significant bit is
> transmitted first. So on the wire the 1's and 0's would be in the same
> order. Here is an excerpt from RFC 2469:
>
> The figure below illustrates the difference between
> canonical and non-canonical form using the canonical form address
> 12-34-56-78-9A-BC as an example:
>
> In memory, 12 34 56 78 9A BC
> canonical: 00010010 00110100 01010110 01111000 10011010 10111100
>
> 1st bit appearing on LAN (group address indicator)
> |
> On LAN: 01001000 00101100 01101010 00011110 01011001 00111101
>
> In memory,
> MSB format: 01001000 00101100 01101010 00011110 01011001 00111101
> 48 2C 6A 1E 59 3D
>
>
> This shows that no matter how the information is stored in memory it looks
> the same on the wire. So if it looks the same on the wire wouldn't an
> adapter pickup the packet and flip the bits in the byte if it needed to.
> Since it on the wire it looks like the bits are in non-canonical format a
> canonical format media would automatically take the first byte and flip
the
> bits and so on, or so I would think.
>
> If anyone can figure out where I am going wrong please let me know. If it
> would be best to talk, email me directly with a daytime phone number and
I
> will call you. Thanks.
> Neil
>
>
>
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