From: Brian Hescock (bhescock@xxxxxxxxx)
Date: Sat Sep 16 2000 - 10:39:37 GMT-3
Sanjay,
The sizes of the two files can be identical in size and still get a bad
checksum. CRC is a complex algorithm that helps determine that a packet is
received in the same way it was sent. Here's a very simplistic example:
01000110 3
10110111 6
01011101 5
11101100 5
23322422
Again, this is a very crude example (CRC is far more complex), but take
the number of ones in each byte and add them up going across. Do the same
thing vertically. Then take these numbers to the right and bottom and use
a forumla to come up with a CRC that would indicate if one of the 1's was
transposed during transmission, etc.
The most common cause of a bad checksum is the copy you originally
downloaded to your tftp server was bad. This could be because either the
image you originally copied was bad or there was a bad circuit somewhere,
etc. It's possible there could be a problem with your flash but that
doesn' happen too often.
Brian
On Fri, 15 Sep 2000, Maljure, Sanjay wrote:
> Hi All
> I am trying to copy an IOS image to the flash of a router. I have tried it
> several times now. From different sources (including another router's flash)
> and everytime, I get the same error message :
>
>
> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> !!!!
> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> !!!!
> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> [OK - 8124000/8388608 bytes]
>
> Verifying checksum... invalid (expected 0x748A, computed 0xEAD8)
> Flash copy took 0:05:52 [hh:mm:ss]
> r8(boot)#
> r8(boot)#sh flash
>
> System flash directory:
> File Length Name/status
> 1 8124000 c2500-js-l_112-19.bin [invalid checksum]
> [8124064 bytes used, 264544 available, 8388608 total]
> 8192K bytes of processor board System flash (Read/Write)
>
> r8(boot)#
>
>
> The size of the file matches perfectly with the file size in the source
> location. But everytime the checksum is failing. Could this be a faulty
> flash???? BTW I haven't played around with this router before and hence
> never personally seen it boot good from an IOS on the flash.
>
> Please help. What could be causing it?
>
> Thanks
> Sanjay
>
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