Firmware update source server is the TFTP server in general with update
files in it's tftproot.
We made some recipes for you how to easily get this service up an running.
Windows users, please, consult our howto "Configuring TFTP server in Windows", Linux users may easily use traditional TFTP server software.
Get TFTP server up and running, put firmware update files into tftproot and check if it's available for download by running
# tftp serverip
in Windows cmd shell or Linux CLI.
> get myupdatefile.itb