Users Guide

executing this action, use the no spanning-tree pvst err-disable cause invalid-pvst-bpdu command. After you
congure 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 dierent 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 miscongurations.
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 dierentiate
BPDUs on each VLAN so that PVST+ does not detect a loop and both ports can remain in a Forwarding state.
Figure 96. 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+ Conguration
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
We are the root of Vlan 5
Configured hello time 2, max age 20, forward delay 15
PVST+ Sample Congurations
The following examples provide the running congurations for the topology shown in the previous illustration.
Example of PVST+ Conguration (R1)
interface GigabitEthernet 1/22
no ip address
switchport
no shutdown
584
Per-VLAN Spanning Tree Plus (PVST+)