Basically there is no such thing as an address by name…it’s always decimal. The dotted-decimal format looks something like “192.168.1.1”. There is a service (DNS) which looks up names and tries to provide dotted-decimal. Without that service the dotted-decimal still works, but names do not (including “tegra-ubuntu”).
Since your tegra-ubuntu is not part of a public network no DNS provider has any idea what address is assigned. It’s up to your host to manually know this, or else it is up to the router to know. It is quite possible the router assigned dotted-decimal but does not know named address. Checking the router logs is the way to go…most routers have a web interface and you can check logs or just directly look somewhere on the router and see what addresses it assigned. If your host is the router then this would be on your host; if this is a router appliance then it would be part of the router. If you can find any kind of log on your router (and I am curious if you have a separate router or if your host is acting as router) it would be of great benefit.
Note that if you can use the 9-pin D-sub connector for serial console (settings 115200 8N1) it would be very beneficial as well since this is immune to many kinds of failures and works even in the boot loader before Linux ever starts.