X1 Gen1 Carbons hang when trying to get a DHCP address through the embedded script

[nappington]

I'm experiencing a very curious problem - I'm using the embedded script method to chainload into iPXE. This is not a problem for any device I try to netboot except for the 2013 X1 Carbons with their proprietary USB NIC dongles

The machines do get an initial DHCP address and pull down iPXE successfully through TFTP. The embedded script loads, but once I try to get a DHCP address either through the DHCP command or the ifopen command the machine hangs and becomes unresponsive. This image shows what happens when I drop down to a shell and try to get a DHCP address. Nothing except for hard resetting the machine works from this point.

A Packet capture shows absolutely zero dhcp discover requests being sent out by the machine itself. when it tries to get a dhcp address

The problem appears to be related with BIOS versions. All machines with UEFI version 2.56 work fine, but the ones with 2.50 or lower fail like this. It seems that 2.56 fixes this issue, but the changelogs haven't been helpful in indicating what it fixed.

I understand that I can the BIOS for each machine with an older UEFI version, but we possess a ridiculously large number of machines that it would be very cost-ineffective, and I'm curious if I can implement iPXE for these machines in a way that allows these X1s to bypass the hanging or if anyone else has experienced this issue before