Re: [Fwd: Crc-32c example in iSCSI spec]

[Mark Bakke <mbakke@cisco.com>]

Steve-

I just ran some Ethernet packets with known CRCs through
my iSCSI/Ethernet CRC generator, and found the same thing
as you did.

All of my examples need to be byte-swapped, along with the
fix I already posted for the all-ones example.  Here is a
new set of examples, which will be in -08.  I also ran
64 bytes of zeroes and ones, which now agree with your
numbers as well.

Thanks again for bringing this up.

--
Mark


     07 CRC Examples 
         
        N.B. all Values are Hexadecimal 
         
          Byte:        0  1  2  3 
         
             0:       01 a0 00 00 
             4:       00 00 00 00 
             8:       00 00 00 00 
            12:       00 00 00 00 
            16:       04 05 00 00 
            20:       00 01 00 00 
            24:       00 00 00 05 
            28:       00 00 00 04 
            32:       2a 00 00 00 
            36:       00 00 00 00 
            40:       80 00 00 00 
            44:       00 00 00 00 
         
           CRC:       93 70 51 db 
         
        32 bytes of zeroes: 
         
          Byte:        0  1  2  3 
         
             0:       00 00 00 00 
           ... 
            28:       00 00 00 00 
         
           CRC:       aa 36 91 8a 
         
        32 bytes of ones: 
  
          Byte:        0  1  2  3 
         
             0:       ff ff ff ff 
           ... 
            28:       ff ff ff ff 
         
           CRC:       43 ab a8 62 
         
        32 bytes of incrementing 00..1f: 
         
          Byte:        0  1  2  3 
         
             0:       00 01 02 03 
           ... 
            28:       1c 1d 1e 1f 
         
           CRC:       4e 79 dd 46 
 



Steve Blightman wrote:
> 
> I believe the examples for the ISCSI CRC  have the wrong endianness.
> 
> As yiou suugested over the phone I ran some Ethernet frames through a
> simulation. I have some difficulty running the exact simulations you
> wanted becuase the minimum size Ethernet frame is 64 bytes.
> 
> However using the Ethernet CRC polynomial,
> Running 64 bytes of 0 onto the wire, we append "36 63 8d 75" onto the
> wire for the CRC - "36" goes out first.
> Running 64 bytes of all 1, we append "ba 87 61 0f" onto the wire - "ba"
> goes out first.
> 
> Using the same logic for the ISCSI polynomial
> Running 64 bytes of 0 I think we should append "67 eb c8 03" - "67"
> going out first
> and running 64 bytes of all 1 we should append "66 4e cd 2f" - "66"
> going out first
> 
> And now for 32 bytes with the ISCSI polynomial
> 
> Running 32 bytes of 0 we should append "aa 36 91 8a" - "aa" going out
> first
> Running 32 bytes of all 1 we should append "43 ab a8 62" - "43" going
> out first
> 
> I don't want to get into an endless endian debate, but I believe it is
> important to get the order of these bytes in the right order, so that we
> can use the same hardware to check as well as to generate CRCs.
> 
> Thanks for your help on this,
> Steve Blightman

-- 
Mark A. Bakke
Cisco Systems
mbakke@cisco.com
763.398.1054