How to add firmware to Broadcom NIC

First, confirm you have the Broadcom NIC

$ lspci | grep 'Ethernet controller'
01:00.0 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme II BCM5709 Gigabit Ethernet (rev 20)
01:00.1 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme II BCM5709 Gigabit Ethernet (rev 20)
02:00.0 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme II BCM5709 Gigabit Ethernet (rev 20)
02:00.1 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme II BCM5709 Gigabit Ethernet (rev 20)

then install the firmware

sudo apt install firmware-bnx2