On a current Catalyst product Is it better to assign an IP address directly to a VLAN interface or to assign an IP address to a Loopback interface that is in a particular VLAN? What are the benefits or pitfalls of either method?
You cannot configure the loopback interface as switchport. Also you cannot configure a SVI ( interface vlan ) as a switchport. So the solution is to configure the IPs on the interface vlan.