Use the CST Configuration page to configure the Common Spanning Tree (CST) settings. The settings and information on this page define the device within the spanning tree topology that connects all STP (Spanning Tree Protocol)/RSTP bridges and MSTP (Multiple Spanning Tree Protocol) regions.
To access this page, click in the navigation menu.
Spanning Tree CST Fields
| Field | Description |
|---|---|
| Bridge Priority | The 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. |
| Bridge Max Age | The amount of time a bridge waits before implementing a topological change. |
| Bridge Hello Time | The amount of time the root bridge waits between sending hello BPDUs. |
| Bridge Forward Delay | The amount of time a bridge remains in a listening and learning state before forwarding packets. |
| Spanning Tree Maximum Hops | The maximum number of hops a Bridge Protocol Data Unit (BPDU) is allowed to traverse within the spanning tree region before it is discarded. |
| BPDU Guard | When enabled, BPDU Guard 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. |
| BPDU Filter | When enabled, this feature filters the BPDU traffic on the edge ports. When spanning tree is disabled on a port, BPDU filtering allows BPDU packets received on that port to be dropped. |
| Spanning Tree Tx Hold Count | The maximum number of BPDUs that a bridge is allowed to send within a hello time window. |
| Bridge Identifier | A unique value that is automatically generated based on the bridge priority value and the base MAC address of the bridge. 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. |
| Time Since Topology Change | The amount of time that has passed since the topology of the spanning tree has changed. |
| Topology Change Count | The number of times the topology of the spanning tree has changed. |
| Topology Change | Whether a topology change is in progress on any port assigned to the CST. If a change is in progress the value is True; otherwise, it is False. |
| Designated Root | The bridge identifier of the root bridge for the CST. The identifier is made up of the bridge priority and the base MAC address. |
| Root Path Cost | The path cost to the designated root for the CST. Traffic from a connected device to the root bridge takes the least-cost path to the bridge. If the value is 0, the cost is automatically calculated based on port speed. |
| Root Port | The port on the bridge with the least-cost path to the designated root for the CST. |
| Max Age | The amount of time a bridge waits before implementing a topological change. |
| Forward Delay | The forward delay value for the root port bridge. |
| Hold Time | The minimum amount of time between transmissions of Configuration BPDUs. |
| CST Regional Root | The bridge identifier of the CST regional root. The identifier is made up of the priority value and the base MAC address of the regional root bridge. |
| CST Path Cost | The path cost to the CST tree regional root. |
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