Why is the protocol down, even though you issued the no shutdown command for interface vlan 99?

At least one device needs to be assigned to a Vlan 99 to bring the protocol up. Assuming that the Status is UP and the protocol is DOWN may mean that there are no ports assigned to Vlan 99 and thus no host assigned to this Vlan.

Answer and explanation:

The protocol of a management interface with VLAN 99 could be "down" because there are no ports assigned to it, meaning there are no hosts assigned to that interface. In this case, the status of the interface can be displayed as "up" regardless of the protocol.

answer///copyrights protects;