A port may only be added to one VLAN untagged. This is
because you can't have two vlans passing traffic over a single link without a VLAN tag on one to
differentiate them on the other end. An error will be thrown when attempting to add a port as untagged to a second VLAN. You can fix this by removing the port from the
original VLAN or add the port as tagged.
X450G2-48t-G4.2 # configure vlan test add port 1 untagged
Error: Protocol conflict when adding untagged port 1. Port 1 is already
untagged in vlan "Default".
Either add this port as tagged or assign another protocol to this VLAN.