I just spent hours recovering from an etherboot loop.
1. Make at least 2 working partitions
2. If Netinstall fails to install the OS, do not try again. Copy the remaining working partition to the erased partition first.
3. If Netinstall stops detecting the routerboard, reboot the PC.
4. If Netinstall fails to install, use a different network adapter (I got it working with Intel over Thunderbolt)