VSX switch with RPVST, as root and nonroot

In the following figure, the VSX pair is configured as a root switch. All the ports of the VSX LAGs, non-VSX LAGs, and orphan ports are in a forwarding state. Bridge Protocol Data Units (BPDUs), generated by a VSX pair, are the same on all ports, including VSX LAG, non-VSX LAG, and orphan. All switches must be in the same MSTP region consisting of the same configuration name and revision number, as set by the spanning-tree config-name <CONFIG-NAME> and spanning-tree config-revision <REVISION-NUMBER> commands.

Definitions of the abbreviations used in the figures provided in this topic
Abbreviation	Definition
AB	Alternate blocking; the port is in a blocked state.
DF	Designated forwarding; the port is in a forwarding state.
RF	Root forwarding; the port is in a forwarding state.

To make the VSX switch root for one or more RPVST instances, set the switch to the lowest bridge identifier for the tree:

For one RPVST instance: switch(config)# spanning-tree vlan 1 priority 1
For more than one RPVST instance: switch(config)# spanning-tree vlan 1-100 priority 1

In the following figure, the VSX pair is not a root switch for STP topology. One of the VSX LAG ports is in the blocking state for resolving an L2 network loop. The VSX LAG port is in a blocking state on both VSX peer switches.