pfSense » pfSense Docs

The definition of Parent Interface on page https://docs.netgate.com/pfsense/en/latest/vlan/terminology.html has a Note saying

"The sole function of the parent interface is, ideally, to be the parent for the defined VLANs and not used directly. In some situations this will work, but can cause difficulties with switch configuration, and it requires use of the default VLAN on the trunk port, which is best to avoid as discussed further in VLANs and Security."

As a relative newbie, I found this exceedingly confusing: it seems to mean that the parent interface is not to be used at all. That's reinforced by the configuration example a couple of pages later at https://docs.netgate.com/pfsense/en/latest/vlan/configuration.html#console-vlan-configuration, which actually shows VLANs being attached to an interface that's down (ie no cable attached). Of course, this reading is complete nonsense, but there's nothing in the definition of Parent Interface that would clarify it. I suggest adding a sentence to the Parent Interface definition along the lines of "The VLAN interface represents all packets tagged with its VLAN ID that are sent or received on the physical connection identified by the parent interface". The first sentence of the Note would be much better stated along the lines of "Ideally, all traffic sent or received on a physical interface used for VLANs should be tagged with one or another VLAN ID, so that no traffic flows through the parent interface as such." The rest of the Note is equally desperately in need of a rewrite, but I have no concrete suggestions there. After that, you should fix the configuration example so that it shows an actually-usable configuration, rather than VLANs attached to an unconnected interface.