Since it seems you have a monitor connected to the server, you can log into the system and using the NetworkManager (underlying framework to manage network connections used by Rockstor and determine the active interface(s) you have by typing:
nmcli device status
Identify the interface that has a connection. Use that connection name to review the profile via:
nmcli -p con show <ConnectionName>
this should give you a screen output with multipe sections. If it’s anything like mine, there will be a list of connection properties, followed by list of properties of the connection type (e.g. 802-3-ethernet), which is then followed by ip4 and ip6 properties. the ip4.method property would show “auto” if it was set to receive its IP address and other settings (e.g. Gateway address) automatically. If it doesn’t, then probably a command line editing is needed (using the nmcli editor). There is a wiki entry for the Networking architecture that you can take a look at:
But I also hope, that somebody else can chime in, especially if there are more effective ways exist to analyze and remedy this.