Does anyone know what filetype or filesystem a router firmware file (one downloaded from manufacturer's site) is usually saved in? Is there a tool (we're not talking about archive tool like zip/7z/rar here) that I could use to unpack/properly repack the firmware file? Reason I'm asking is because I want to fiddle around with the default dyndns services in the firmware, probably add some changes to them and have my router flushed with the modified firmware. The router doesn't support custom and fancy 3rd party firmwares, hence the reason I need to mod the manufacturer's stock firmware.
EDIT -- When I posted this question, I thought the dyndns updater in the router firmware was just a simple bash script and I figured I could do some quick edit on the script but turns out that it's actually a binary app when I checked all the processes running in the router, so this question is not relevant anymore