PVRST is an enhancement of RSTP, which works in conjunction with VLANs to provide better control over traffic in the network. A separate spanning tree is maintained for each active VLAN in the network, providing:
Load balancing through multiple instances of the spanning tree.
Fault tolerance (because failure of one spanning tree instance does not affect other spanning trees).
Rapid reconfiguration support through RSTP.
Note - PVRST is not a standards based protocol, it is a Cisco proprietory protocol. Each vendor's implementation will be different but is expected to be largely compatible.
In this fairly common PVRST based configuration, we define eight VLANs (200-203, 300-303). Four VLANs (300-303) are named external-vlan-n. The Ethernet core switch is configured as the root bridge for VLANs 300-303. The other four VLANs (200-203) are named internal-vlan-n. Switch ToR72p-1 is configured as the root bridge for VLANs 200-203. Internal VLANs (200-203) are not configured in the core switch to avoid LAN traffic from reaching the core network. The internal VLAN traffic will not go beyond the distribution layer ToR72p-n switches because switch ToR72p-1 is the root for the internal VLANs.
The internal VLANs normally carry traffic such as live migration, web engineering, ZFS or NFS application data, cluster heartbeat, and so on. External VLANs carry traffic that wants to reach the outside world.
The default vlan 1 can be changed to a different VLAN if required, but you must make the change before starting a configuration and restart SEFOS for the change to take effect.