I strongly suspect this is connected to Ubuntu Xenial (was having similar problems when trying to enable DevStack+Ironic+PXE on Xenial).
There are some (all in general?) *.c32 modules to copy to tftp root along with pxelinux.0. From my experience with Virtual BMs in devstack on xenial, ldlinux.c32 was exactly the file needed.
I strongly suspect this is connected to Ubuntu Xenial (was having similar problems when trying to enable DevStack+Ironic+PXE on Xenial).
There are some (all in general?) *.c32 modules to copy to tftp root along with pxelinux.0. From my experience with Virtual BMs in devstack on xenial, ldlinux.c32 was exactly the file needed.
For the record this path upstream tackles exactly the same problem https:/ /review. openstack. org/#/c/ 326024
Denis, afaik 9.1 still uses Trusty, so it should not be affected