After one of my WiSM2’s crashed yesterday I had a request from Cisco TAC to supply the coredump from the controller. Whilst attempting to do this I ran into issues utilising TFTP which was due to the fact that my TFTP server didn’t support the size of the file I was trying to upload to it.

I have since found:
The original protocol has a transfer file size limit of 512 bytes/block x 65535 blocks = 32 MB. In 1998 this limit was extended to 1468 bytes/block x 65535 blocks = 93 MB by TFTP Blocksize Option RFC 2348.
Source: https://en.wikipedia.org/wiki/Trivial_File_Transfer_Protocol

Now the process to upload to TFTP/FTP a coredump or crashfile etc is detailed on the following Cisco Site:

https://supportforums.cisco.com/document/139766/how-find-retrieve-wlcs-crash-coredump-itss-flash-external-ftptftp-server

What I had happen:

I ran the command to see if there was a core dump file following the WiSM2 crash:

(controller)> show coredump summary

I then setup the WLC to transfer the coredump via TFTP

(Controller)>transfer upload datatype coredump
(Controller)>transfer upload _8.0.120.30_controller_1478497361.gz 
(Controller)>transfer upload mode tftp
(Controller)>transfer upload serverip

Then issued the upload start command

(Controller)>transfer upload start

And then Press Y when prompted

As you can see the transfer failed, I then repeated the same command but changed the datatype to Crash File and it worked successfully

At the time I didn’t have a FTP server available that had security access for the WLC to FTP the file across. After much reading and going back and forth with TAC it was suggested that the coredump file could not be transferred off the box.

The next day when I hadn’t of been working 14 hours straight and dealing with 2 major incidents, I built up an FTP server in a subnet with rights for the WLC to FTP to and tried FTPing the coredump file

(Controller)>transfer upload datatype coredump
(Controller)>transfer upload _8.0.120.30_controller_1478497361.gz 
(Controller)>transfer upload mode ftp
(Controller)>transfer upload serverip

It was successful, I then set out to find why the TFTP didn’t work and was advised by a colleague that TFTP had a file size limitation, and a quick Google search found the 32/93MB size limitations.

I can tell you it would have made it a lot easier if I had of known the TFTP limitation that night as we spent nearly an hour or two trying to make TFTP work.