Reference Guide

– Disable the shutdown-on-violation command on the interface (the no spanning-tree
stp-id portfast [bpduguard | [shutdown-on-violation]] command).
– Disable spanning tree on the interface (the no spanning-tree command in INTERFACE mode).
– Disabling global spanning tree (the no spanning-tree command in CONFIGURATION mode).
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, Dell Networking OS places the port in an Error-Disable state. This behavior might result
in the network not converging. To prevent Dell Networking OS 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 109. PVST+ with Extend System ID
• Augment the bridge ID with the VLAN ID.
PROTOCOL PVST mode
extend system-id
Example of Viewing the Extend System ID in a PVST+ Configuration
Dell(conf-pvst)#do show spanning-tree pvst vlan 5 brief
VLAN 5
Executing IEEE compatible Spanning Tree Protocol
Root ID Priority 32773, Address 0001.e832.73f7
Root Bridge hello time 2, max age 20, forward delay 15
Bridge ID Priority 32773 (priority 32768
sys-id-ext 5), Address 0001.e832.73f7
Per-VLAN Spanning Tree Plus (PVST+)
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