VLAN interface line protocol status

Ever created a vlan interface and it's showing that the interface status is up-down?

Just now, I've created a vlan interface and its physical link status is immediately up. Unfortunately, the line protocol status is always down.

Come to think, it might need some ports to be assigned, so I assigned an Fa 0/1 to Vlan20. However, the luck has not yet to come.

It turned out that it needs some devices to also attached to that interface. So my conclusion is, if the link of the physical port is up-up, then the vlan protocol status will then go up. Someone else might have an explanation to this, but I don't.

This is the debug:

%LINK-5-CHANGED: Interface FastEthernet0/1, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan20, changed state to up
RT: interface Vlan20 added to routing tableRT: SET_LAST_RDB for 172.16.71.0/24
NEW rdb: is directly connected

RT: add 172.16.71.0/24 via 0.0.0.0, connected metric [0/0]

See .. my new static route is also added to the table :)