Debian buster EFI netinstall timeout getting grubx64.efi

[Michael Kesper <mkesper@schokokeks.org>]

Dear list members,

please excuse my ignorance, but I cannot figure out how to netboot Debian buster.
Can you give me pointers to a working setup for multiple distributions (e.g. Debian 9 and Debian 10)
with EFI boot?

I come as far as getting the GRUB2 shell displayed (version 2.0.2+dfsg1-16).
I can see "Fetching Netboot Image" (see screenshot), then after 30s the Grub shell gets displayed.
I can see no more files being tried to download, no NAKs.

Setup:
Supermicro Server with E5-2600, boot mode: UEFI

Network boot gets started by choosing UEFI: IP4 Intel... in boot menu.
F12 does not work (might only try IPv6?)

dhcpd: isc-dhcpd-4.1.1-P1
tftp-hpa 0.49, with remap, with tcpwrappers
(Yes, CentOS host...)

Relevant dhcp setup:

if exists dhcp-parameter-request-list {
   # Always send the PXELINUX options (specified in hexadecimal, ie: 208 = 0xd0, 209 = 0xd1, etc.)
   option dhcp-parameter-request-list = concat(option dhcp-parameter-request-list,d0,d1,d2,d3);
 }

group  {
    use-host-decl-names on;
    max-lease-time 300;
    default-lease-time 120;
    next-server 10.45.10.5;

  host ssfnkvm112 {
    option host-name "myhost";
    hardware ethernet 0C:C4:...;
    fixed-address 10.45.10.32;
    filename "debian-10/bootnetx64.efi";
  }
}

tftproot is:
/var/lib/tftproot

As there are different distributions served from here, I created a folder
/var/lib/tftproot/debian-10
and extracted netboot.tar.gz below it.

I added several symlinks, last setup was this:
(Yes, probably the server should not be run as root, but that's another issue...)

# ls -lh /var/lib/tftpboot/debian-10
total 8.0K
lrwxrwxrwx 1 root root   36 May  9 11:34 boot-screens -> debian-installer/amd64/boot-screens/
lrwxrwxrwx 1 root root   37 May  8 11:15 bootnetx64.efi -> debian-installer/amd64/bootnetx64.efi
drwxrwxr-x 3 root root 4.0K Apr 10 20:55 debian-installer
lrwxrwxrwx 1 root root   27 May  9 10:59 grub -> debian-installer/amd64/grub
lrwxrwxrwx 1 root root   34 May  9 10:58 grubx64.efi -> debian-installer/amd64/grubx64.efi
lrwxrwxrwx 1 root root   47 May  8 13:46 ldlinux.c32 -> debian-installer/amd64/boot-screens/ldlinux.c32
lrwxrwxrwx 1 root root   33 May  8 13:46 pxelinux.0 -> debian-installer/amd64/pxelinux.0
lrwxrwxrwx 1 root root   35 May  8 13:46 pxelinux.cfg -> debian-installer/amd64/pxelinux.cfg
-rw-rw-r-- 1 root root   55 Apr 10 20:55 version.info


Excerpt from logs:
May  8 16:02:07 ssfnctl111 dhcpd: DHCPREQUEST for 10.45.10.32 (10.45.10.5) from 0c:c4:xxx via eth0
May  8 16:02:07 ssfnctl111 dhcpd: DHCPACK on 10.45.10.32 to 0c:c4:xxx via eth0
May  8 16:02:07 ssfnctl111 in.tftpd[21355]: RRQ from ::ffff:10.45.10.32 filename debian-installer/amd64/bootnetx64.efi
May  8 16:02:07 ssfnctl111 in.tftpd[21355]: tftp: client does not accept options
May  8 16:02:08 ssfnctl111 in.tftpd[21356]: RRQ from ::ffff:10.45.10.32 filename debian-installer/amd64/bootnetx64.efi
May  8 16:02:08 ssfnctl111 in.tftpd[21357]: RRQ from ::ffff:10.45.10.32 filename debian-installer/amd64/grubx64.efi
(Nothing re tftp afterwards)

Thanks
Michael

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