I have hit a Dell UEFI BIOS (PowerEdge R720 with
Broadcom LAN-on-motherboard 2 x 10GbE 2 x 1GbE) which
loads GRUB by PXE but GRUB itself hits "error: couldn't send network packet" and cannot download grub.cfg.
GRUB shows 8(!) efinet cards; there are four physical NICs,
each with 2 mac addresses (one for LAN, one for iSCSI offload).
This is a Broadcom BCM57800.
However efinet0 efinet1 are given the same mac address
similarly for efinet2, efinet3 etc etc instead, the mac addresses should differ by 1.
The box boots fine with grub-legacy, and an older BIOS/NIC firmware (in fact that is how I got it to install). After the BIOS/NIC firmware upgrade the problems started.
net_ls_addrs, net_ls_cards net_ls_routes don't look suspicious (except for the duplicate mac addresses).