New for Nodegrid 6.0 and later, you can now use any interface in Iptables firewall or NAT rules.  You can use interfaces that don't show in the interface drop-down menu.  You can also use an interface that doesn't exist yet, such as VTI interfaces for IPsec tunnels that may not be available yet or started yet.

To use an interface that doesn't show in the drop-down or doesn't exist yet, simply create a rule as normal and then select "Custom" from the drop-down and enter the name of the interface.

From the CLI, here is an example adding an ACCEPT rule for INPUT chain for vti01, and interface that doesn't exist yet.