The FreeBSD pxeboot binary wants to include the loader from a NFS share. If mounting the share fails, the system will halt and needs a hard reboot. In order to propagate the loader via TFTP you need to recompile the binary. Therefore, you will have to install the FreeBSD sources and edit your /etc/make.conf. Insert
into the file. This will make pxeboot to be compiled without NFS and with TFTP support. Then change into
and make the sources. A new file pxeboot will appear, which is able to load the loader via TFTP. One very annoying thing still happens with the new pxeboot (at least till 7.2): Pxeboot will still try to mount the NFS share and will get the loader after the NFS timeout occured (60 seconds on my systems).