You have configured a Cisco Catalyst switch to perform Layer 3 routing via an SVI and you have
assigned that interface to VLAN 20. To check the status of the SVI, you issue the show interfaces
vlan 20 command at the CLI prompt. You see from the output display that the interface is in an
up/up state. What must be true in an SVI configuration to bring the VLAN and line protocol up?

A.
The port must be physically connected to another Layer 3 device.

B.
At least one port in VLAN 20 must be active.

C.
The Layer 3 routing protocol must be operational and receiving routing updates from
neighboring peer devices.

D.
Because this is a virtual interface, the operational status is always in an “up/up” state.

Explanation:
The SVI interfaces have to fulfill the following general conditions to be up/up:
• VLAN exists and is in active status on the switch VLAN database.
• VLAN interface exists on the router and is not administratively down.
• At least one L2 (access port or trunk) port exists and has a link up on this VLAN. The latest
implementation of the autostate feature allows synchronization to Spanning-Tree Protocol (STP)
port status.
• A VLAN interface will be brought up after the L2 port has had time to converge (that is, transition
from listening-learning to forwarding). This will prevent routing protocols and other features from
using the VLAN interface as if it were fully operational. This also prevents other problems, such as
routing black holes, from occurring.
• At least one L2 (access port or trunk) port is in spanning-tree forwarding state on the VLAN.
So for SVI to bring the vlan and line protocol up at least one port in that vlan must be active.
Reference:
http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a0080160b14.shtml