Reference Guide

752 | Per-VLAN Spanning Tree Plus (PVST+)
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PVST+ in Multi-vendor Networks
Some non-Dell Force10 systems which have hybrid ports participating in PVST+ transmit two kinds of
BPDUs: 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 this
happens, FTOS places the port in error-disable state. This behavior might result in the network not
converging. To prevent FTOS from executing this action, use the command
no spanning-tree pvst
err-disable cause invalid-pvst-bpdu. After you configure this command, if the port receives a PVST+
BPDU, the BPDU is dropped, and the port remains operational.
PVST+ Extended System ID
In Figure 37-5, 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 the above scenario, however, PVST+ can be
employed to avoid potential misconfigurations.
If PVST+ is enabled on the Dell Force10 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 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 forwarding state.
Figure 37-5. PVST+ with Extend System ID
FTOS Behavior: Regarding bpduguard shutdown-on-violation behavior:
1 If the interface to be shutdown is a port channel then all the member ports are disabled in the hardware.
2 When a physical port is added to a port channel already in error disable state, the new member port will also be disabled
in the hardware.
3 When a physical port is removed from a port channel in error disable state, the error disabled state is cleared on this
physical port (the physical port will be enabled in the hardware).
4 The reset linecard command does not clear the error disabled state of the port or the hardware disabled state. The
interface continues to be disables in the hardware.
The error disabled state can be cleared 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 stp-id portfast [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).