I'm confused.
I always assumed I could configure this on a 3750 switch, just like on a 6500:
interface FastEthernet1/0/1 description LINK to XXX IP address 10.4.1.1 255.255.255.0
But, it won't accept the command on the 3750, instead, to have a routable interface, I have to do this:
interface FastEthernet1/0/1 description LINK to XXX switchport access vlan 2
interface Vlan2 ip address 10.4.1.1 255.255.255.0
And it works just fine.
What simple, obvious thing have I missed here?