TrueNAS setup is fairly straight forward, and well documented. However, there are a few things the documentation does not cover.

When TrueNAS is first installed, it assumes you will be doing the configuration from the WebUI. However, you can use the cli menu for some basic things.

In my case, I had several instances where I was installing TrueNAS on a network that used DHCP, Link Aggregation (LAGG) and Virtual LAN's (VLAN's) defined on the network switch. The CLI is not exactly self explanatory on how this works.

1. Delete all interfaces (menu option 1, choose interface, then delete). This is the important step
2. Create LAGG (I think that is menu option 3?)
3. Create the VLAN on the LAGG you created (menu option 2?)
4. Set up DCHP on the VLAN you created (menu option 1, do NOT delete, just modify)