How to turn your OpenWRT router into a PXE server for hardware installations with netboot.xyz

USB Stick preparation

I used a spare USB-Stick that I formated with ext4 and lableing the partition tftp.

mkfs.ext4 -L tftp /dev/sdXX

Replace /dev/sdXX with your partition path. ie /dev/sdc1 OpenWRT preparation

This was done on OpenWRT Version 19.07

opkg update
opkg install usbutils kmod-usb-storage block-mount kmod-fs-ext4 wget
mkdir -p /mnt/usb/

wget package is needed because the dropbear version does not support SSL Mount USB-Stick reboot persistent¶

uci set fstab.@mount[0].label=tftp
uci set fstab.@mount[0].target=/mnt/usb
uci set fstab.@mount[0].options=noatime,nodiratime
uci commit

block mount

Get PXE images

Instead of pulling each OS image individually I use netboot.xyz. netboot.xyz is basically a menu wrapper for all kinds of operating systems.

cd /mnt/usb/

Legacy (PCBIOS) iPXE Bootloaders

wget --no-check-certificate https://boot.netboot.xyz/ipxe/netboot.xyz.kpxe

UEFI iPXE Bootloaders

wget --no-check-certificate https://boot.netboot.xyz/ipxe/netboot.xyz.efi

Configure dnsmasq

Unfortunately I was only able to set one bootfile.

The linuxserver.io documentation states that multiple entries should be possible. This didn't work for me =(

uci set dhcp.@dnsmasq[0].enable_tftp=1
uci set dhcp.@dnsmasq[0].tftp_root=/mnt/usb/
uci set dhcp.@dnsmasq[0].dhcp_boot=netboot.xyz.kpxe
uci commit
/etc/init.d/dnsmasq restart

Finally a crucial but hard to find configuration change for OpenWRT

Disable the LAN interface to announce itself as a Local IPv6 DNS server which in turn somehow conflicted with the iPXE DNS lookup (even though booted in IPv4 mode).

Available through the OpenWRT interface. Network -> Interfaces, LAN -> Edit, DHCP Server -> IPv6 Settings. Untick this box if ticked.