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.

Table 23: 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 or switch(config)# spanning-tree vlan 10,20,30 priority 1

The priority parameter has a range of 0 to 15 for setting the priority of the RPVST. The priority value is configured as a multiple of 4,096 (Default: 8). For example, when priority parameter is set as 1, the priority value is 4,096. When the priority parameter is set to 2, the priority value is 8,192. By default the priority parameter is 8, so the default priority value is 32,768.

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.