Does anyone know what the second least significant bit does at 0x53 on the x520? i.e. I'm wondering the difference between 0xFC/0xFD and 0xFE/0xFF is. Obviously the least significant bit is the "Allow unapproved SFP+", but what's the one next to it?
I ran ethtool, saw either 0xFC or 0xFE on a Dell 0C63DV and in my excessive enthusiasm just slammed 0xFF in there, despite the clear warning in the OP (yes, I'm stupid). A reboot didn't bring up the link and I realized I wasn't sure if it was FC or FE so I put 0xFD in there, still didn't work but it wound up being a port speed problem on the switch, once that was corrected everything was fine with 0xFD.
Now I'm second guessing myself if it was originally 0xFC or 0xFE and what if anything is going to be affected if I flipped that second bit as well. The links are up but I haven't done much testing with actual traffic yet.
EDIT: Oh, and by the way, I did this using ethtool on ESXi 6.5, the "ethtool" instructions in the OP worked perfectly. Just had to use "vmnic0" as the interface name. Reading the value back from "vmnic1" once I wrote to "vmnic0" also showed the value I wrote, obviously it's just one ROM for both interfaces.
EDIT 2: Spoke too soon. This does NOT seem to work with ESXi 6.5 build 17477841 in a Dell Poweredge r620. I think when I first saw it work I had a connection up with DAC cables and then hot plugging the unsupported SFP+ modules in worked for some reason. But after a reboot it won't load the driver if it sees the module, and even hot plugging after another power off reboot seems to be hit and miss whether or not it will accept the module or just shut down the port. I checked this with the 0C63DV LOM as well as a separate x520-da2 card, both were set to 0xfd, and I did check after a power off reboot to make sure that the change had persisted. Take this with a grain of salt, but it did not work for me. Firmware on both cards is Dell 19.5.12. I'm just going to use DAC cables but hope this is useful for someone.
I ran ethtool, saw either 0xFC or 0xFE on a Dell 0C63DV and in my excessive enthusiasm just slammed 0xFF in there, despite the clear warning in the OP (yes, I'm stupid). A reboot didn't bring up the link and I realized I wasn't sure if it was FC or FE so I put 0xFD in there, still didn't work but it wound up being a port speed problem on the switch, once that was corrected everything was fine with 0xFD.
Now I'm second guessing myself if it was originally 0xFC or 0xFE and what if anything is going to be affected if I flipped that second bit as well. The links are up but I haven't done much testing with actual traffic yet.
EDIT: Oh, and by the way, I did this using ethtool on ESXi 6.5, the "ethtool" instructions in the OP worked perfectly. Just had to use "vmnic0" as the interface name. Reading the value back from "vmnic1" once I wrote to "vmnic0" also showed the value I wrote, obviously it's just one ROM for both interfaces.
EDIT 2: Spoke too soon. This does NOT seem to work with ESXi 6.5 build 17477841 in a Dell Poweredge r620. I think when I first saw it work I had a connection up with DAC cables and then hot plugging the unsupported SFP+ modules in worked for some reason. But after a reboot it won't load the driver if it sees the module, and even hot plugging after another power off reboot seems to be hit and miss whether or not it will accept the module or just shut down the port. I checked this with the 0C63DV LOM as well as a separate x520-da2 card, both were set to 0xfd, and I did check after a power off reboot to make sure that the change had persisted. Take this with a grain of salt, but it did not work for me. Firmware on both cards is Dell 19.5.12. I'm just going to use DAC cables but hope this is useful for someone.
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