Freeradius Dhcp and Tftp Pxe.

[CpServiceSPb .]

I have Freeradius 3.0.19 acting as AAA and Dhcp, there is also atftpd with
iPXE bootloader for PXE booting.

Such clients are defined by %{string:&DHCP-Vendor-Class-Identifier} and
should get address from IP Pool from flat text file.
Other clients (for example Windows) receive IP successfuly.
But PXE clients don' t get IP at all.
Why ?

If address assignment is set up via static mac-ip bindings (mac2ip file) IP
is assigned but boot file undionly.pxe is not found.
Because Freeradius adds "M-^?" (in ASCII without quotes) or in 0x4d2d5e3fff
between file name undionly.pxe and trailing zero.
Why ?
And how do it correct ?