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Verifying IOS Images

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Wed, 11/18/2009 - 18:38
Sep 25th, 2009
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Verifing the IOS image is a smart thing to do. It's relatively easy for the  image to get corrupt, especially if you use TFTP across a WAN link. You should  verify the image once you download it from Cisco. That way you don't send a  bad image to a router. I use a free program called HachCalc (http://www.slavasoft.com/hashcalc/index.htm)  to verify the image.


hash_calc.GIF

When you download IOS from Cisco they provide the MD5 hash so you can verify  the image doesn't get corrupt during the download. Here you can see the MD5  hash.


cisco_md5.gif

Once you transfer the image to flash, you should verify it again on the  router. Here's how to do that.


3745RTR#dir
Directory of flash:/

1 -rw- 37576908 Jun 13 2008 09:07:40 -05:00 c3745-advipservicesk9-mz.124-18b.bin

63864832 bytes total (26284032 bytes free)


MAD2#verify /md5 flash:/c3745-advipservicesk9-mz.124-18b.bin
.........................................................................................
.........................................................................................
.........................................................................................
.........................................................................................
.........................................................................................
.........................................................................................
verify /md5 (flash:/c3745-advipservicesk9-mz.124-18b.bin) =  98f47ca4de03a28a7c6988469e99ef8f


3745RTR#


I have also created a spreadsheet so you can paste in values and have it  verify the hash values and give you nice visual confirmation. Download it here https://packetpros.com/EngTools/hash.xls.

hash_excel.bmp


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