Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 741

PVST+ in Multi-Vendor Networks Some non-Dell Networking systems which have hybrid ports participating in PVST+ transmit two kinds of BPDUs: an 802.1D BPDU and an untagged PVST+ BPDU. Dell Networking systems do not expect PVST+ BPDU (tagged or untagged) on an untagged port. If this situation occurs, the system places the port in an Error-Disable state. This behavior might result in the network not converging. To prevent the system from executing this action, use the no spanning-tree pvst err-disable cause invalid-pvst-bpdu command. After you configure this command, if the port receives a PVST+ BPDU, the BPDU is dropped and the port remains operational. Enabling PVST+ Extend System ID In the following example, ports P1 and P2 are untagged members of different VLANs. These ports are untagged because the hub is VLAN unaware. There is no data loop in this scenario; however, you can employ PVST+ to avoid potential misconfigurations. If you enable PVST+ on the Dell Networking switch in this network, P1 and P2 receive BPDUs from each other. Ordinarily, the Bridge ID in the frame matches the Root ID, a loop is detected, and the rules of convergence require that P2 move to blocking state because it has the lowest port ID. To keep both ports in a Forwarding state, use extend system ID. Extend system ID augments the bridge ID with a VLAN ID to differentiate BPDUs on each VLAN so that PVST+ does not detect a loop and both ports can remain in a Forwarding state. Figure 103. PVST+ with Extend System ID • Augment the bridge ID with the VLAN ID. PROTOCOL PVST mode extend system-id Per-VLAN Spanning Tree Plus (PVST+) 741