How to build an ISO with undionly?

[robinsmidsrod]

That is not possible. Using the UNDI driver is only possible when you boot using PXE chainloading. See http://ipxe.org/howto/chainloading for how to set up your network for that. If you don't know how to setup the basic services for supporting network booting, have a look at the various tutorials linked from http://networkboot.org/.

Also, some Broadcom devices are supported directly by iPXE (normally the ones using the tg3 Linux driver). The ones normally using the bnx2 Linux driver are not (yet) supported by iPXE.