Recovery mode is only for flashing, and after a flash completes, then the Jetson self-reboots. Once the reboot completes the time has arrived for networking and optional package installs. More recent releases also require setting up a first boot login name/password, and so once you’ve done this, then you can log in and run those commands again. At this point JetPack/SDK Manager can add extra packages.
Normally one would connect both the host PC ethernet and the Jetson ethernet to a router. A router would automatically assign an address at each boot and you wouldn’t need to manually configure this.
You can manually configure a static IP address for host and/or Jetson…the online Ubuntu documents for this work since the Jetson’s Ubuntu is no different than a host PC’s Ubuntu.
Alternately, the micro-B USB cable provided with the dev kit provides a “virtual” wired ethernet over USB if you want to use that. The flash software does not care if it is real ethernet or virtual ethernet. In the case of the virtual USB ethernet there is a built in router for address assignment. The Jetson becomes 192.168.55.1, and the host PC with the USB connector to the Jetson becomes 22.214.171.124 (gigabit is faster, but USB2 isn’t too bad). In the case of using the micro-B USB cable you might need to tell the host PC to allow the ethernet device, but most of the time it will “just work”.
Do note that you can run extra package install at a later time and deselect flash so long as you finished the first boot account creation.