Existing assigned interface to VLAN

[Jonttu]

I know this should be fairly basic thing to do but for some reason I fail to wrap my head around it and decide how to do it easiest way.

Basically I have a physical port igb1 used for my server so it has been assigned in interfaces without VLANs and have own DHCP etc normally. But now I have a need for more subnets and I have run out of ports on my OPNSense so I need to tranform this existing interface into a VLAN so I can then get the existing network and a new one from the same port and then in VLAN aware switch handle rest.

But what is the most effective way of transforming this existing network into a VLAN network. What I mean by that is that I would like to keep the existing DHCP static mappings and the same ip subnet on the existing network so minimal changes done to it.

[Patrick M. Hausen]

Just assign the logical name in Interfaces > Assignments to a VLAN interface and all address configuration, DHCP, firewall rules ... will follow.

That's why this extra level of abstraction exists 

[Jonttu]

Of course it was that simple  I thought too complicated. Thank you kind person for your help!

[dseven]

I probably shouldn't admit how long it took to dawn on me that the assignments / device column contains drop-down menus. I somehow got it in my head that once an assignment is made, the only way to change it would be to delete and create a new assignment. In fairness, I think the section at the bottom that says "No devices available for assignment" should really be something like "No unassigned interfaces"