What is dhcp_boot setting?

I've been experimenting with PXE boot configuration, and after trying several different configurations, it seems that setting option dhcp_boot '<path>,<server name>,<server ip>' works. This has to be set in the dnsmasq configuration in /etc/config/dhcp.

I've also tried setting options 66 and 67 alone, and I can't boot successfully with those two alone. It seems that dhcp_boot is setting 66 to the server name and 67 to the path, but I'm not sure what is being set with the server ip value.

I've done some digging, having use nmap's broastcast-dhcp-discover script, and dhcpdump to try and see what values are returned by the server, but I don't see an option value with the server IP address.

Does anyone know what option is being set with the server ip address value from dhcp_boot?

I think I answered my own question' appears to be setting next-server value.