Per-VLAN Spanning Tree Plus (PVST+) | 411PVST+ in Multi-vendor NetworksSome non-Dell Force10 systems that have hybrid ports participating in PVST+, transmit two kinds ofBPDUs: an 802.1D BPDU and an untagged PVST+ BPDU.Dell Force10 systems do not expect PVST+ BPDU (tagged or untagged) on an untagged port. If thishappens, FTOS places the port in the Error Disable state. This behavior might result in the network notconverging. To prevent FTOS from executing this action, use the no spanning-tree pvst err-disable causeinvalid-pvst-bpdu command. After you configure this command, if the port receives a PVST+ BPDU, theBPDU is dropped and the port remains operational.PVST+ Extended System IDIn Figure 23-6, ports P1 and P2 are untagged members of different VLANs. These ports are untaggedbecause the hub is VLAN unaware. There is no data loop in the above scenario; however, you can employPVST+ to avoid potential misconfigurations.If you enable PVST+ on the Dell Force10 switch in this network, P1 and P2 receive BPDUs from eachother. Ordinarily, the Bridge ID in the frame matches the Root ID, a loop is detected, and the rules ofconvergence require that P2 move to the Blocking state because it has the lowest port ID.To keep both ports in Forwarding state, use Extend System ID. Extend System ID augments the Bridge IDwith a VLAN ID to differentiate BPDUs on each VLAN so that PVST+ does not detect a loop, and bothports can remain in Forwarding state.FTOS Behavior: Regarding the bpduguard shutdown-on-violation behavior:1 If the interface to be shutdown is a port channel, all the member ports are disabled in the hardware.2 When you add a physical port to a port channel already in Error Disable state, the new member port idalso disabled in the hardware.3 When you remove a physical port from a port channel in Error Disable state, the Error Disabled state iscleared on this physical port (the physical port is enabled in the hardware).4 You can clear the Error Disabled state with any of the following methods:• Perform a shutdown command on the interface.• Disable the shutdown-on-violation command on the interface (no spanning-tree pvst edge-port[bpduguard | [shutdown-on-violation]]).• Disable spanning tree on the interface (no spanning-tree in INTERFACE mode).• Disabling global spanning tree (no spanning-tree in CONFIGURATION mode).
