By default ssh daemon runs and accepts connections. The default account on all Ubuntu machines is “ubuntu” with login password “ubuntu”.
By default networking uses and configures via DHCP. Any router should see and assign an address when the Jetson boots.
Unrelated to Linux or DHCP, only the router will know the address assigned. No name server knows the address, and so no name lookup is possible by default…only the dotted-decimal address format is available. To find the machine via a named address, such as “tegra-ubuntu”, either the router has to know this name and be accessed from inside the router’s private network, or else the machine accessing the Jetson has to be configured to know the named alias.
If the machine has freshly arrived, check your router for the assigned address. Ping implies the same address as used for ssh. If you have used the JetPack utility, then there may have been network setup changes on both the Jetson and the host computer which ran JetPack, especially changes to allow naming the Jetson as “tegra-ubuntu”.
ssh remembers keys the first time an access is approved. Should those keys change, access will be denied until the old key is removed. Flashing or using JetPack for a new install may change keys at either the Jetson side or the host side. Your address “192.168.0.102” closing like that may imply keys or setup have changed…such as via JetPack or flash altering keys.
NOTE: Getting to the point where the ssh port gives a reply before closing the connection tells you the ssh server is running…without the ssh server the connection would never have occurred.
If you use a serial console, then all networking and video issues will be irrelevant, allowing you to set things up or see logs as to why ssh aborted. You could also do a fresh flash, as flash has a setup step in it equivalent to running the NVIDIA-INSTALLER script prior to flash and having this transfer over to the Jetson.