Per-VLAN Spanning Tree (PVST)

Note

Extreme Networks has adopted 802.1s in place of PVST. The PVST protocol is only supported on legacy Matrix switches (Matrix E6, Matrix E7 (2nd & 3rd Gen) SmartSwitch 2000 and SmartSwitch 6000.)

Per-VLAN Spanning Tree (PVST) is the Extreme Networks non-standard implementation of multiple Spanning Trees, developed prior to ratification of the IEEE 802.1s MST standard. PVST does not interoperate with other vendors‘ non-standard implementations of multiple Spanning Trees.

Like 802.1s, PVST allows for multiple instances of Spanning Tree to exist within a LAN, with one VLAN mapped to each instance. There are three significant benefits to PVST:

• It utilizes load sharing, where each interswitch link forwards traffic for at least one Spanning Tree instance.
• A re-span on a particular Spanning Tree instance only affects the VLAN that was mapped to that instance.
• The scalability of topologies can be extended much greater than single 802.1D Spanning Tree domains.
  

  Note

  Since GVRP assumes a single Spanning Tree per domain, GVRP cannot be run in PVST regions of the network topology.

The PVST BPDU destination address is 01:00:1d:00:00:05 and includes the VLAN it is servicing in the packet, regardless if the packet has an 802.1Q tag or not.

The VLAN header reads, in hex, 82 00 03 followed by the VLAN ID, in hex. For example, VLAN 10 shows up as 00 0a after the VLAN header.

All ports continue to send out IEEE BPDUs with a destination address of 01:80:c2:00:00:00 out all other ports, plus the PVST BPDU for that specific VLAN. If the port is in the default VLAN, the port will only send out an IEEE BPDU. This makes it possible to keep a mesh of IEEE switches as they join the default VLAN's IEEE Spanning Tree, that can exist off the same interface as a PVST switch, running one or more VLANs through a tagged or untagged interface. This topology will form a Root Bridge for the IEEE VLAN for all VLANS that do not have their own Spanning Tree, and another Spanning Tree for each VLAN that has its own Spanning Tree. VLANs that are not added to their own Spanning Tree will remain in the default Spanning Tree and, therefore, will form a Spanning Tree with all other IEEE switches in the network.