PVST+ and R-PVST+ overview

The Per-VLAN Spanning Tree Plus (PVST+) protocol runs a spanning tree instance for each VLAN in the network. The version of PVST+ that uses the RSTP state machine is called Rapid-PVST Plus (R-PVST+). R-PVST+ has one instance of spanning tree for each VLAN on the device.

Both the STP and the RSTP build a single logical topology. A typical network has multiple VLANs. A single logical topology does not efficiently utilize the availability of redundant paths for multiple VLANs. A single logical topology does not efficiently utilize the availability of redundant paths for multiple VLANs. If a port is set to the blocked state or the discarding state for one VLAN (under the STP or the RSTP), it is the same for all other VLANs. PVST+ builds on the STP on each VLAN, and R-PVST+ builds on the RSTP on each VLAN.

PVST+ R-PVST+ provide interoperability with Cisco PVST and R-PVST and other vendor switches which implement Cisco PVST or R-PVST. the PVST+ and R-PVST+ implementations are extensions to PVST and R-PVST, which can interoperate with an STP topology, including MSTP (CIST), on Extreme and other vendor devices sending untagged IEEE BPDUs.

PVST+ and R-PVST+ guidelines and restrictions

Consider the following when configuring PVST+ and R-PVST+:

Extreme supports PVST+ and R-PVST+ only. The PVST and R-PVST protocols are proprietary to Cisco and are not supported.
A port native VLAN is the native VLAN ID associated with a trunk port on an Extreme switch. This VLAN ID is associated with all untagged packets on the port. The default native VLAN ID for a trunk port is 1.
IEEE compliant switches run just one instance of STP protocol shared by all VLANs, creating a Mono Spanning Tree (MST). A group of such switches running a single spanning tree forms an MST region.
You can configure up to 256 PVST+ or R-PVST+ instances. If you have more than 256 VLANs configured on the switch and enable PVST then the first 256 VLANs are PVST/+ or R-PVST+ enabled.
In PVST/+ or R-PVST+ mode, when you are connected to a Cisco or MLX switch, the Cisco proprietary MAC address to which the BPDUs are sent/processed must be explicitly configured on a per-port basis.
In PVST/+ or R-PVST+ mode, when you connect to a Cisco switch using a trunk port, the Extreme switch must have a native VLAN configured on the trunk port (same configuration as on the other side).
A Common Spanning Tree (CST) is the single spanning tree instance used by Extreme switches to interoperate with 802.1q bridges. This spanning tree instance stretches across the entire network domain (including PVST, PVST+ and 802.1q regions). It is associated with VLAN 1 on the Extreme switch.
In order to interact with STP and IEEE 802.1q trunk, PVST evolved to PVST+ to interoperate with STP topology by STP BPDU on the native or default VLAN.
A group of switches running PVST+ is called a PVST+ region.

For more information about spanning trees, see the introductory sections in the Spanning Tree Protocol chapter.

PVST+ and R-PVST+ parameters

The parameters you would normally set when you configure STP are applicable to PVST+ and R-PVST+. Before you configure PVST+ or R-PVST+ parameters see the sections in the Standing Tree Protocol chapter explaining bridge parameters, the error disable timeout parameter and the port channel path cost parameter.

There is one parameter that can be configured in R-PVST+ that is not available in STP or PVST+; the transmit hold count. This parameter configures the BPDU burst size by specifying the maximum number of BPDUs transmitted per second for before pausing for 1 second. The range is 1 through 10 while the default is 6. See the section Configuring R-PVST+ for the procedure to configure this parameter.