When you are new to creating VLANs on your network, you may wonder about the necessary steps in order to create a properly functioning VLAN. If you set up OPNsense with one WAN and one LAN interface, it is kind enough to set up a basic configuration for the LAN interface with DHCP enabled and a single firewall rule that allows access to the Internet. You can consider this configuration to be a “flat” network, which means that every device is on the same network and can communicate.
For the uninitiated, VLANs are Virtual Local Area Networks. Think of them as logically separate networks that are similar in concept to physically separated networks. The biggest difference is that you do not need to put network devices on physically separate switches or other network hardware. VLANs are both economical and convenient. It is economical since you do not need to purchase extra hardware and convenient since your network devices can be physically located anywhere yet still be grouped in logically separate networks.