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Configuring a core dump for a Cisco (IOS) Switch or Router

Step 1:

Because a crash may be imminent can we enable a debug called “debug sanity”, basically this has the switch perform additional checks on its memory.  After you apply this please keep an eye on the CPU by doing show process cpu history.  If this debug causes a huge spike then please do “undebug sanity”.  Also, if the switch reloads this debug will be automatically removed.  In the event of a crash we might have more information about what is causing the issue.

Step 2:

Enabling a core dump in the event of a crash:

There are 3 main ways to do it, depending on one's environment and what is easiest.

The easiest way is dumping to flash. Depending on the platform this could be flash: bootflash: or disk0:   By default a core dump sent to flash is compressed but you likely need a hundred MB of flash free, depending on the platform.  Time required to write a corefile to flash vs. writing a corefile via ftp will vary based on the size of the file.  Lab tests show the following times for writing 3.5 GB worth of corefiles:


1005532950 bytes

248 seconds

4059003 bytes/sec


1006632960 bytes

2051 seconds

490801 bytes/sec

This is with an FTP server on a local segment with average response times around 1 ms, increasing the number of hops or increasing the response time will decrease the performance.

*Actual results may vary*

Instructions for all three methods follow:


config t

ip ftp username [login-name]   

   (optional, not needed if anonymous ftp is enabled on the destination server)

ip ftp password [login-pass]   

   (optional, not needed if anonymous ftp is enabled on the destination server)

exception protocol ftp

exception region-size 65000

exception dump [ip-address]    

    (If there is no ftp username/pass it will attempt anonymouse FTP.)


write mem


config t

exception protocol tftp

exception region-size 65000

exception dump [ip-address]


write mem

Note: Please test FTP/TFTP server configuration to ensure it works correctly.

copy run tftp:


copy run ftp:

Then after some prompting you should see something like:

Writing c7600-confg !

2781 bytes copied in 0.944 secs


conf t

exception flash all [path]

                  (bootflash:, disk0:, etc)

Finally, what do you do with the large file that is generated and is too large for email?

Please edit the filename to include your SR Number then you can send the core dump files to Cisco through anonymous FTP. 

The FTP server is at the following location (directory /incoming )

Please respond with feedback if this document assist you or if you feel this document contains inaccuracies or needs additional information.

Thank you,

Brian Hardenstein



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