Explanation The default spanning-tree mode in Cisco switch is PVST+. This spanning-tree mode is based on the IEEE 802.1D standard and Cisco proprietary extensions. PVST+ is same as standard IEEE 802.1D but it runs on each VLAN. In the output we see the line "Spanning tree enabled protocol ieee" under "VLAN 20" so it can say the switch is running in PVST+ mode.