If the client has had iPXE burned into its ROM (or is a VM that uses iPXE as the PXE "ROM"), special handling is needed because in this mode the client is using iPXE native drivers and chainloading to a UNDI stack won't work.

If the client identifies as "Tinkerbell", we've already chainloaded this client to the full-featured copy of iPXE we supply.

ArchToBootFile maps supported hardware PXE architectures types to iPXE binary files.

Handler holds the configuration details for the running the DHCP server.

Netboot holds the netboot configuration details used in running a DHCP server.

UserClass is DHCP option 77 (https://www.rfc-editor.org/rfc/rfc3004.html).