4-11
Switching Features
Spanning Tree
Hello Time The interval between periodic transmissions of STP BPDUs by designated ports. This value is set
to 2 seconds and cannot be changed.
Forward Delay The amount of time a bridge remains in a listening and learning state before forwarding packets.
The range is from 4 to 30 seconds and the default is 15 seconds.
Bridge Priority A value that helps determine which bridge in the spanning tree is elected as the root bridge during
STP convergence. A lower value increases the probability that the bridge becomes the root bridge.
the default value is 32768.
BPDU Guard When enabled globally, the switch can disable edge ports that receive BPDU packets. This prevents
a new device from entering the existing STP topology. Thus, devices that were originally not a
part of STP are not allowed to influence the STP topology. When disabled, an edge port that receives
a BDPU becomes a non-edge port, which can affect the STP topology.
When enabling BPDU Guard, also ensure that the desired interfaces are operating as edge ports
by enabling the Admin Edge Port mode for each of those interfaces.
This feature is disabled by default.
BPDU Filter When enabled, this feature filters the BPDU traffic on edge ports. When spanning tree is disabled
on a port, BPDU filtering allows BPDU packets received on that port to be dropped.
When enabling BPDU Filter, also ensure that the desired interfaces are operating as edge ports by
enabling the Admin Edge Port mode for each of those interfaces.
This feature is disabled by default.
Spanning Tree Interface Status—The following fields list the interfaces on which the feature is enabled. See Table
4-7 on page 4-14 for descriptions of these features.
Root Bridge
Identifier
The bridge ID of the root bridge for the spanning tree. The identifier is made up of the bridge
priority and the base MAC address. When electing the root bridge for the spanning tree, if the
bridge priorities for multiple bridges are equal, the bridge with the lowest MAC address is elected
as the root bridge.
Root Guarded
Interfaces
A list of the interfaces for which Root Guard is enabled.
TCN Guarded
Interfaces
A list of the interfaces for which TCN Guard is enabled.
BPDU Flood
Enabled
Interfaces
A list of the interfaces for which the BPDU Flood feature is enabled.
BPDU Filtered
Interfaces
A list of the interfaces for which BPDU Filter is enabled.
Spanning Tree Interface Settings—This page also displays a table with configured settings for each interface. See
Table 4-7 on page 4-14 for descriptions of these settings. This table displays the following additional field.
Port Role The role of the port with respect to spanning tree functionality, which is one of the following:
• Root: A port on the non-root bridge that has the least-cost path to the root bridge.
• Designated: A port that has the least-cost path to the root bridge on its segment.
• Alternate: A blocked port that has an alternate path to the root bridge.
• Backup: A blocked port that has a redundant path to the same network segment as another port
on the bridge.
• Disabled: The port is administratively disabled and is not part of the spanning tree.
Field Description
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