Hopefully, this article helps others who encounter this "fun," random issue that I recently experienced. Here's my story!
We received a new shipment of Dell R640s - the same exact order that we had been purchasing repeatedly for a couple years now. Upon racking them and setting up iDRAC, we went to PXE install ESXi 6.7 U3 (Dell custom image). Unfortunately, after the NIC received its DHCP offer and the initial boot files over TFTP, the ESXi installer would show up and hang. It would simply be stuck loading the kernel (usually b.b00 or tboot.00).
After troubleshooting literally everything I could think of, we were stuck. Here's what we tried:
So, as seen by the abbreviated list above, I tried almost everything and was certain that it was a CPU or NIC option that was causing the issue. I decided to downgrade the new R640's Broadcom 57412 (advanced 10/25Gb) NIC's firmware to match the older R640's and...it worked! Do I know the root cause and why this solution works? Nope. I intend to read the changelogs and try to identify what triggered this but for now, here's the solution!
While I feel like many people won't hit this issue, I felt the need to post just in case it helps at least one other person. I was going crazy trying to figure it out!