Recommendations for 802.1q, PVST+, MST interoperability when connecting two devices via an 802.1q trunk, one device running PVST+ and one running MST the Following guidelines should be followed:
Make sure that the native vlan at both ends of the 802.1q trunk is the same
Make sure that the trunk is carrying vlan 1 (in order to have a common spanning tree)
Make sure that the native vlan of ports being connected by the trunk is vlan 1
Connect PVST+ devices to the MST cloud always using trunks never using access ports.
It is important to ensure that the native vlan be vlan 1 to avoid confusion about the root election on the native VLAN.
It is important to connect to the MST cloud using trunks (of 802.1q type) because the "Cisco PVST+
802.1q BPDUs" need to be tunneled on the Common Spanning Tree and the Common Spanning Tree can only be build by carrying VLAN 1.
