After upgrading to ESXi 5.5 or 6, Emulex 10G nic does not work. If you run esxcfg-nics -l, the NICs still have link. If you check the module, it is loaded but it won’t work. It won’t pass traffic.
For 5.5, we found a workaround in the community forum by way of disabling elxnet and enabling be2net driver followed by a reboot. Prior to upgrade, in 5.1, be2net was the driver but upon upgrading to 5.5 or 6, the driver changes to elxnet.
The be2net trick does not work for ESXi 6 though. We had to upgrade the Emulex NIC firmware to 11.x or 10.x depending on the NIC model. You can use vmkchdev -l | grep vmnicX to find the vendor, sub-vendor IDs etc. which you can use to lookup the NIC in VMware compatibility guide. Some of the Emulex 10G are certified only upto 5.5 U3 as of this writing.
Until we encountered this I did not know Emulex was acquired by Avago Technologies. So if you search Emulex 10G firmware, you will end up at Avago website. The firmware is packed in a bootable ISO which is simple to use and fast to load. If the ISO doesn’t find the device it is intended for, it will tell you. For example, 11.x firmware was unable to find a compatible device because the NIC was an OC10 and not OC11.