Ok now I know what @n8v8r means.
First of all there is nothing like untagged vlan with VID. That is like having TCP stack without lower layer like IP. It does not make sense. You just don’t understand
swconfig configuration as it seems.
Ok so what following configuration meant with swconfig:
config switch_vlan option device 'switch0' option vlan '3' option ports '5t 2' option vid '3'
First of all port
5 is CPU port. This instructed switch to create VLAN over port
2 and CPU port where traffic on CPU will be tagged. That means that it will be received on CPU port with tag
In case of DSA you can just use plain
lan2 to have same functionality.