I recently upgraded to a Netgear R6220. I have previously used OpenWRT on a Netgear WNDR3700, and wanted to do the same here. The main purpose for switching from OEM to open source firmware was to enable internet service through the USB port. I can' t get decent broadband internet at my house, but I can get decent cellular data signal. I have a wireless hot spot (Netgear AirCard 815S) that supports USB tethering. I use the hotspot modem to talk to the cell tower, then feed the signal to the USB port on the router.
I was doing the same thing on the WNDR3700, but had a lot of trouble finding an open source distribution that would work on that router and talk to the hotspot modem. I tried DD-WRT, and also OpenWRT, but both would not connect to the modem. I eventually found and tried an Australian distribution of OpenWRT called ROOter. Current version is based on OpenWrt 18.06.1. There seems to be a lot of people down under with a similar problem - not much cable lines once you get outside of the cities, but cellular is available. That distribution does a good job of interfacing with many different cellular modems, and supports the USB interface method.
So the whole setup has now been shifted to the new R6220 router, and it's running great. On a good day, I can make 100 Mbps on the cellular modem (4G LTE service). The router has much greater bandwidth and can pass virtually all of that to the devices with little loss. I'm hoping the cellular provider upgrades to some level of 5G service in the next year or so. At that point I'll have to upgrade to a 5G hotspot modem, but otherwise the rest of the setup should be good.
Got a question about install procedure for OpenWRT (specifically the ROOter distribution) on this router, since I don't think the instructions on the ROOter pages say much. I went to the openwrt.org pages, and found general instructions as shown below. I did this a few months back, so I don't guarantee that I remember all the details (although I kept notes).
1. From the ROOter site, download the firmware package. Latest is something like "R6220-GO2019-03-10" (downloads as folder)
2. Enable debug mode on the router: http://<router_ip>/setup.cgi?todo=debug
<router_ip> is normally 192.168.1.1, unless you have changed it for some reason.
You should see a response "Debug Enabled"
3. Copy the rootfs.bin and kernel.bin files to a USB flash drive.
4. Telnet to <router_ip> and login as root (either default password=admin or whatever you changed it to)
5. Connect the USB drive to the USB port on the router.
Check that the drive is recognized and mounts. For the original Netgear firmware, the mountpoint should be at /mnt/shares. If you run:
ls /mnt/shares
you should see the USB drive. If you don't see the USB drive after a reasonable wait period since you plugged it in, check the /dev directory and see if it is listed there. If it is you may be able to mount it manually:
create a mount directory: mkdir /mnt/shares/<usb_drive>
mount the drive: mount /dev/<usb_drive> /mnt/shares/<usb_drive>
6. Enter the USB drive:
cd /mnt/shares/<usb_drive>
7. Install the binaries and reboot:
mtd_write write rootfs.bin Rootfs
mtd_write write kernel.bin Kernel
reboot
I didn't initially understand what "mtd_write" does. Run "mtd_write --help" to get a basic explanation. I believe I had to leave the USB drive plugged in as it read info from the other files in the download package after the reboot (But not positive on that point). Once the router is fully up and running on the new firmware, you should be able to see the web login page, and login to the web interface. At that point, you can unmount the USB drive and remove it.
As I said - it's been a while since my original install. Hopefully this covers the basics. Check the openwrt.org page for the device for more details if you need them.
Thanks for the installation procedure and for your experience of this process. I went through this to flash my r6220 and it worked. I was able to log into the UI and set things up. The next day I ran into an issue went I turned it on and tried to log into the UI. I it would not log in. All the router lights were on like normal. I could ping the router address. I ended up using SSH to connect to the router and reset to default settings. That got the router backup and logged into UI. The seems to be working fine and I get the internet from the modem just fine. I have found that the 2.4Ghz AP is acting finicky. It will only initially connect if it has a signal with full bars. Once it connects then it will stay connected. But for example, if I leave home and come back my phone wont connect until it gets full bars again. I plan to reinstall the firmware through the UI to see if that will fix it. I could not find if there are different versions of this router to see if that would be the problem. I am open for any suggestions.
I've had minor problems along the way, but nothing that matches what you describe. I have occasional problems - more just a slow reaction - when I wake my desktop up from sleep and it takes unexpectedly long for the main, hardwired ethernet connection to become active.
One good source of help with ROOter is the forum they run at:
https://forums.whirlpool.net.au/forum-replies.cfm?t=2689577&p=-1&#bottom
There is a lot of ongoing discussion there, and you may be able to get better help from people there.
An update to this story - I have intentionally waited to do the latest upgrade to the R6220 firmware because I need this unit for work now (thanks COVID) and couldn't take the risk. But most of that has settled down now, and I decided to take plunge this past week. I was able to use the built-in 'upgrade' utility in the Rooter firmware - worked great. Now I'm upgraded to OpenWRT 18.06.7 and things generally seem to be running fine.