A network engineer has configured a Layer 3 switch with SVIs for VLANs 4 and 5. Hosts in the subnets using VLANs 4 and 5 can ping each other with the Layer 3 switch routing the packets. The next week, the network engineer receives a call that those same users can no longer ping each other. If the problem is with the Layer 3 switching function, which of the following could have caused the problem?
(Choose two answers.)

(A) A shutdown command issued from VLAN 4 configuration mode
(B) VTP on the switch removing VLAN 5 from the switch’s VLAN list
(C) 1 out of 10 working VLAN 4 access ports failing due to physical problems
(D) A shutdown command issued from VLAN 6 configuration mode

A and B are the correct answers.

A Layer 3 switch will not route packets on a VLAN interface unless it is in an up/up state. A VLAN interface will only be up/up if the matching VLAN (with the same VLAN number) exists on the switch. If VTP deletes the VLAN, then the VLAN interface moves to a down/down state, and the routing on that interface stop. Also, disabling VLAN 4 with the shutdown command in VLAN configuration mode also causes the matching VLAN 4 interface to fail, which makes routing on interface VLAN 4 stop as well.

A Layer 3 switch needs only one access port or trunk port forwarding for a VLAN to enable routing for that VLAN, so nine of the ten access ports in VLAN 4 could fail, leaving one working port, and the switch would keep routing for VLAN 4.

A shutdown of VLAN 6 can’t affect the VLANs 4 and 5.