This is under development. Don't expect anything until 12.2. Until then, you can manually setup up bridge interfaces and set iocage to use them with startup scripts and manuel configuration. I recently saw another member with VLANs and jails. Search and I'm sure you will find it. I don't know what you say about IP ranges... Either assign it statically or use DHCP. FreeNAS oen not have a DHCP server built in. If you want an IP for a particular VLAN, once the jail is connected to the VLAN, it will request DHCP from that layer 2 network.