Using Apple Thunderbolt 2 Ethernet adapter on Ubuntu 20.04

Question

I installed Ubuntu 20.04 Server on my 2014 Macbook Pro and it all works great with the USB to ethernet adapter. However, when I try to use the Thunderbolt 2 to ethernet adapter I can't get the network connection to work. Running ip a shows (what I think is) the Thunderbolt interface (ens9) as DOWN, so I ran sudo ip link ens9 up. Then the Macbook shows up as a device in my router, but I still can't access it (have a web server running on it that works fine with the USB adapter). Running ping google.com gives: ping: google.com: Temporary failure in name resolution.

I haven't installed any drivers, just simply plugged in the Thunderbolt adapter and booted up. Would be very happy for some help to troubleshoot. Thanks in advance!

EDIT: Running cat /etc/netplan/*.yaml gives:

# This is the network config written in 'subiquity'
network:
  ethernets:
    enx00f76f6f62ca:
      dhcp4: true
    version: 2

And running sudo lshw -C network gives:

  *-network
       description: Network controller
       product: BCM4360 802.11ac Wireless Network Adapter
       vendor: Broadcom Inc. and subsidiaries
       physical id: 0
       bus info: pci@0000:03:00.0
       version: 03
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress bus_master cap_list
       configuration: driver=bcma-pci-bridge latency=0
       resources: irq:18 memory:b0600000-b0607fff memory:b0400000-b05fffff
  *-network DISABLED
       description: Ethernet interface
       product: NetXtreme BCM57762 Gigabit Ethernet PCIe
       vendor: Broadcom Inc. and subsidiaries
       physical id: 0
       bus info: pci@0000:0a:00.0
       logical name: ens9
       version: 00
       serial: 18:7e:b9:0a:c7:d6
       capacity: 1Gbit/s
       width: 64 bits
       clock: 33MHz
       capabilities: pm vpd msi msix pciexpress bus_master cap_list rom ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt 1000bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=tg3 driverversion=3.137 firmware=57762-a1.10 latency=0 link=no multicast=yes port=twisted pair
       resources: irq:19 memory:bcc00000-bcc0ffff memory:bcc10000-bcc1ffff memory:b0c00000-b0c0ffff

Answer 1

If sudo lshw -C network is correctly showing that the Thunderbolt 2 to ethernet adapter as ens9, then your /etc/netplan/*.yaml should look like this...

network:
  version: 2
  renderer: networkd
  ethernets:
    ens9:
      dhcp4: true
      optional: true

sudo netplan generate

sudo netplan apply

reboot