STP Status and Global Settings

Spanning Tree Protocol (STP) protects a Layer 2 Broadcast domain from Broadcast storms by selectively setting links to standby mode to prevent loops. In standby mode, these links temporarily stop transferring user data. After the topology changes so that the data transfer is made possible, the links are automatically re-activated.

STP provides a tree topology for any arrangement of switches and interconnecting links, by creating a unique path between end stations on a network, and thereby eliminating loops.

The STP Status and Global Settings page contains parameters for enabling the required STP mode. Use the STP Interface Settings page, RSTP Interface Settings page, and MSTP Properties page to configure each mode, respectively. To set the STP status and global settings, follow these steps:

Procedure

Step 1

Click Spanning Tree > STP Status & Global Settings.

Step 2

Enter the parameters.

Global Settings:

Spanning Tree State

Select to enable on the device.

STP Loopback Guard

Select to enable Loopback Guard on the device.

STP Operation Mode

Select an STP mode.

BPDU Handling

Select how Bridge Protocol Data Unit (BPDU) packets are managed when STP is disabled. BPDUs are used to transmit spanning tree information.

  • Filtering-Filters BPDU packets when Spanning Tree is disabled on an interface.

  • Flooding-Floods BPDU packets when Spanning Tree is disabled on an interface.

Path Cost Default Values

Selects the method used to assign default path costs to the STP ports. The default path cost assigned to an interface varies according to the selected method.

  • Short-Specifies the range 1–65,535 for port path costs

  • Long-Specifies the range 1–200,000,000 for port path costs

    Bridge Settings:

Bridge Settings:

Priority

Sets the bridge priority value. After exchanging BPDUs, the device with the lowest priority becomes the Root Bridge. In the case that all bridges use the same priority, then their MAC addresses are used to determine the Root Bridge. The bridge priority value is provided in increments of 4096. For example, 4096, 8192, 12288, and so on.

Hello Time

Set the interval (in seconds) that a Root Bridge waits between configuration messages.

Max Age

Set the interval (in seconds) that the device can wait without receiving a configuration message, before attempting to redefine its own configuration.

Forward Delay

Set the interval (in seconds) that a bridge remains in a learning state before forwarding packets.

Designated Root / Bridge ID

The bridge priority concatenated with the MAC address of the device.

Root Bridge ID

The Root Bridge priority concatenated with the MAC address of the Root Bridge.

Root Port

The port that offers the lowest cost path from this bridge to the Root Bridge.

Root Path Cost

The cost of the path from this bridge to the root.

Topology Changes Counts

The total number of STP topology changes that have occurred.

Last Topology Change

The time interval that elapsed since the last topology change occurred. The time appears in a days/hours/minutes/seconds format.
Step 3

Click Apply. The STP Global settings are written to the Running Configuration file.