RPVST+

Rapid Per VLAN Spanning Tree+ (RPVST+) is an updated implementation of STP (Spanning Tree Protocol). It enables the creation of a separate spanning tree for each VLAN on a switch, and ensures that only one active, loop-free path exists between any two nodes on a given VLAN.

Spanning tree protocols are used to prevent loops from occurring when multiple paths exist between the devices on a network. They are also used to provide redundancy, enabling data to use an alternate path when one link to a device fails. For example, in the following topology several paths exist between each switch.

The topology has four switches running RSTP. Switch “A” is the root switch. To prevent a loop, RSTP blocks the link between switch “B” and switch “D”. There are two VLANs in this network (VLAN 10 and VLAN 20). Since RSTP does not have VLAN intelligence, it forces all VLANs in a layer 2 domain to follow the same spanning tree.

There will not be any traffic through the link between switch “B” and switch “D” and therefore the link bandwidth is wasted. On the other hand, RPVST+ runs different spanning trees for different VLANs.

RVPST+ creates a spanning tree for VLAN 10.

RVPST+ creates another spanning tree for VLAN 20.

The two topologies above are the same as the first topology, but now the switches run RPVST+ and can span different trees for different VLANs. Switch A is the root switch for the VLAN 10 spanning tree and switch D is the root switch for the VLAN 20 spanning tree. The link between switch B and switch D is only blocked for VLAN 10 traffic but VLAN 20 traffic goes through that link. Similarly the link between switch A and switch C is blocked only for VLAN 20 traffic but VLAN 10 traffic goes through that link. Here, traffic passes through all the available links, and network availability and bandwidth utilization increase.

The following figure shows a further example of shared links and redundant path-blocking in a network running RPVST+.

In the factory default configuration, spanning tree operation is disabled. Configuring the spanning tree mode as RPVST+ on a switch and then enabling spanning tree automatically creates a spanning tree instance for each VLAN on the switch. Configuration with default settings is automatic, and in many cases does not require any adjustments. This includes operation with spanning tree regions in your network running STP, MSTP, or RSTP.

Also, the switch retains its currently configured spanning tree parameter settings when spanning tree is disabled. Thus, if you disable, then later re-enable spanning tree, the parameter settings will be the same as before spanning tree was disabled.

RPVST+ interoperates with devices that run legacy IEEE 802.1D STP.

RPVST+ applies one RSTP tree per-VLAN. Each of these RSTP trees can have a different root switch and span the network through shared or different links.

NOTE:

The switch automatically senses port identity and type, and automatically defines spanning tree parameters for each type, and parameters that apply across the switch. Although these parameters can be adjusted, HPE strongly recommends leaving these settings in their default configurations unless the proposed changes have been supplied by an experienced network administrator who has a strong understanding of RPVST+ operation.

The switch supports 64 spanning tree instances.