[syslinux] core_udp_sendto:no mapping on PXE boot

[Corneel Soete]

Hello,

I have been trying to run a PXE boot on a Lenovo Thinkpad t470s with 
cloud-init. The idea is that we can autoinstall all new laptops that 
come in (will mostly be t470s). Both the uefi and legacy boot are giving 
me problems. On a VM legacy boot works perfectly but UEFI hangs after

Getting cached packet
My IP is 172.16.62.104

On the thinkpad however, the legacy boot has problems while downloading 
the ubuntu-desktop package and afterwards wont even boot into ubuntu 
(even when I try to do an install without autoinstall, I am able to 
fully install ubuntu but afterwards not able to boot into it). UEFI on 
the thinkpad is even worse, it will get to the getting cached packet 
part but after keeps sending the same messages until after a few minutes 
the laptop just restarts.

 >>Start PXE over IPv1

Sation IP address is

Getting cached packet:
My IP is 172.16.62.104
core_udp_sendto: stalling on configure with no mapping
core_udp_sendto: stalling on configure with no mapping
core_udp_sendto: stalling on configure with no mapping
core_udp_sendto: stalling on configure with no mapping
core_udp_sendto: stalling on configure with no mapping
core_udp_sendto: stalling on configure with no mapping
core_udp_sendto: aborting on no mapping
core_udp_sendto: stalling on configure with no mapping
core_udp_sendto: stalling on configure with no mapping
...

The files are being served our server via dnfmasq which is set up as a 
proxy dhcp server and tftp server. We are using syslinux6.03 for the 
kernel files (I have also tried with 6.04 which instead of restarting 
the "core_udp_sendto: stalling on configure with no mapping" lines, 
would just go onto trying to boot via ipv6, not finding anything and 
restarting again). I know not all my problems have to do with syslinux 
but from what I found online at least the part of not being able to get 
into the PXE boot menu might be.

The UEFI BIOS version is N1WET66W (1.45) for the thinkpad.

I have been searching for two entire days now and found an old post on 
this thread with a similar problem in the archives but it ends before a 
solution was found.

I hope someone is able to help me.

Kind regards,

Corneel