Hello, to answer to your question, if you assign the F option, the interface is marked as Forbidden, it means that port is not able to join the VLAN even if it is was dynamically added using a protocol such as GVRP. I hope this helps, thanks Marco  
I've been battling with some of the shortcomings of this model (like not being able to put a management IP on anything but VLAN 1) and I've seen some weird "leakage" between VLANs. I think one thing I saw was the result of a config mistake - a port was untagged for TWO VLANs at the same time, which shouldn't really be possible, but it had VLAN 1 and VLAN 2 both with a "U" when each respective VLAN was selected in the VLAN Membership page. Even after fixing that, I was seeing something odd - two switches, each with only two VLANs and a single cable between them to provide management access (one is an internal network, the other is external). When looking at the dynamic address table on one switch, on the port linked to the other, I saw two MACs. I was expecting just one - the other switch, but I also saw a MAC from a different VLAN... That seems bad? Anyhow, my original question here since the documentation only spends one sentence on this is when setting up port membership, there are 4 options: "unselected", "T" (tagged), "U" (untagged), and "F" ("The interface is denied membership to a VLAN"). What does "The interface is denied membership to a VLAN" mean? "A VLAN"? which one? Is this to explicitly block ingress or egress traffic from the selected VLAN? When is it to be used? Any examples for when it would be used?
PowerConnect 2848 what is "F" in VLAN config used for?