If I attempted to manually set the DNS servers

Model: C6300 / Firmware: V3.01.12

Posted this in another thread, but this is the original thread that gave me the idea that kicked this journey off.

I ended up here because I had the same issue.  If I attempted to manually set the DNS servers but let the remainder of the IP settings be gathered by DHCP from the cable provider, the device would quietly reboot and the setting did not save.  I did find a workaround with some ideas thrown out in other threads and hopefully I documented enough of the process to help someone else out.  I have cut out the failure conditions and just left in what I think would work, YRMV.

1. Power down device and disconnect RG-6
2. Power on device and log into Netgear Genie (admin portal)
3. Advanced :: Setup :: Internet Setup
   1. Internet IP Address :: Use Static IP Address (used generic RFC-1918 IP information)
   2. Domain Name Server (DNS) Address :: Use These DNS Servers (set primary, secondary, and tertiary)
   3. Hit Apply and device did a clean reboot (with UI elements) at this point -- all settings persisted
   4. Internet IP Address :: Get Dynamically from ISP
   5. Hit Apply ... clean reboot -- all settings appeared to revert
4. Connected RG-6 cable back into modem and waited for device to train
5. Checked back in Internet Setup and manual DNS settings persisted

I have a sneaking suspicion that what's happening is a simple bug in the UI elements that configure these settings.  They were probably tested with fully DHCP or fully static configurations, but not with a mixture of both.  There may be a firmware patch available, but the DOCSIS specification puts device firmware updates square in the hands of the ISP.  If the ISP does not actually use these devices out in the wild, there is really no reason for them to provision newer firmware for them (assuming they even keep up with firmware patches in the first place).  Being that this is the only major issue I've had with the device (aside from perceived slow page load times until I disabled the Media Server), I think I'll be keeping it.  Hopefully the steps above will help someone else so they will want to keep theirs as well.