[hackler756]

Download https://github.com/jclehner/nmrpflash
and the dependency https://nmap.org/npcap/#download

nmrpflash uses tftp and the max. filesize is 32MB.
if the firmware image is larger, nmrpflash will report a rollover error during firmware upload.

due to the filesize limitation, download exactly this dd-wrt image 02-08-2021-r45711
https://download1.dd-wrt.com/dd-wrtv2/downloads/betas/2021/02-08-2021-r45711/netgear-r6800/factory-to-ddwrt.img

Connect the router LAN Port 1 directly with your PC. PC LAN interface should have DHCP configured.

Command Prompt as Administrator

# list the network interfaces
nmrpflash.exe -L

in my case eth7

# recover the router
nmrpflash.exe -i eth7 -f factory-to-ddwrt.img

In my case, dd-wrt was installed before and the config (nvram) survived the debricking.
or
without previous dd-wrt installation or after router reset using reset button at the back for 5+ seconds...
after the reboot, router should come online with IP 192.168.1.1, set login and password

02-08-2021-r45711 httpd is quite unstable and crashes a lot.
now navigate directly to the firmware upgrade page using the link http://your_router_ip_address/Upgrade.asp
and upgrade to 11-12-2025-r62606 (last release with kernel 4.14)
https://download1.dd-wrt.com/dd-wrtv2/downloads/betas/2025/11-12-2025-r62606/netgear-r6800/r6800-webflash.bin

restore the nvram config from your backup ...

At the time of this post, current releases for R6800 are broken after kernel upgrade to 6.12.
That's how I ended up here ...

see https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=341078

[kernel-panic69]

Thanks for posting this. But we have been seeking serial logs for what is broken on the Linux 6.12 builds since the shift. Can't fix anything without logs. I think BrainSlayer has an R6800 or similar in hand, but I guess he hasn't tested the more recent images. I know he has asked that I test the WNDR3700v5 and I haven't found the mood. I do know that a reset is required after flashing the 6.12 builds.

[hackler756]

current release 04-20-2026-r64533 boots up with kernel 6.12 on Netgear R6800

serial console logs are posted here
https://forum.dd-wrt.com/phpBB2/viewtopic.php?p=1325208#1325208