Connectivity Guide

The show spanning-tree {brief | details | active} command displays the following information:
Flush Interval 200 centi-sec, Flush Invocations 32
Flush Indication threshold 2
To clear MAC addresses:
● RSTP invokes a port-based MAC flush to clear the MAC address table entry for that port.
● MSTP invokes (VLAN-list associated to the instance, port) based flush to clear the MAC address table entry for that
instance, port.
● RPVST invokes (VLAN, port) based flush to clear the MAC address table entry for that VLAN, port.
By default, this feature is enabled for RSTP, RPVST and MSTP. This feature is very useful in a scalable topology with MSTP &
RPVST (multi-instance), where multiple MAC flush calls are invoked.
RSTP
RSTP allows per port-based flush until the number of calls sent is equal to the MAC flush threshold value that you have
configured.
When the number of calls that are sent reaches the configured threshold, RSTP ignores further per-port based flush and starts
the MAC flush timer. When the timer expires, RSTP invokes an entire table flush, where it requests one flush for all the ports.
RSTP is single instance and hence MAC flush optimization is not required. However, to enable this feature, configure the
MAC flush timer to a non-zero value. This configuration is applied globally and applies for RSTP, MSTP, and RPVST. This
configuration is retained when you change the STP mode.
For RSTP, the threshold is set to a higher value (65,535) because RSTP does not require this optimization. Even when this
feature is enabled, the global flush is invoked only after the flush count reaches 65,535.
MSTP
MSTP allows (VLAN-list, port) based flush until the number of calls sent is equal to the MAC flush threshold value that you have
configured.
When the number of calls exceed the configured threshold, MSTP ignores further (VLAN-list, port) based flush and starts the
MAC flush timer. When the timer starts, the system blocks all further flush indications. When the timer expires for that specific
instance, the system triggers instance-based flushing.
The default MAC flush threshold value for MSTP is 5.
RPVST
RPVST allows (VLAN, port) based flush until the number of calls sent is equal to the MAC flush threshold value that is
configured.
When the number of calls sent exceeds the configured threshold, RPVST ignores further (VLAN, port) based flush and starts
the MAC flush timer. When the timer starts, the system blocks further flush. When the timer expires for that specific instance,
the system triggers VLAN-based flushing.
By default, the MAC flush threshold value is set to 5. However, Dell EMC recommends that you configure this value based on
the number of ports that participate in the STP topology.
MST commands
errdisable detect cause bpduguard
Configures the port to be shut down or moves the port to blocked state on detecting a BPDU guard violation.
Syntax
errdisable detect cause bpduguard
Parameters None
Default Enabled
Command Mode CONFIGURATION
Usage
Information
This command applies only to STP-enabled ports. The command takes effect only when BPDU guard is
configured on a port.
314 Layer 2