3 Configuring the Switch

new root port is selected from among the device ports attached to the network. (References to “ports” in this section mean “interfaces,” which includes both ports and trunks.)

•Hello Time – Interval (in seconds) at which the root device transmits a configuration message.

•Forward Delay – The maximum time (in seconds) the root device will wait before changing states (i.e., discarding to learning to forwarding). This delay is required because every device must receive information about topology changes before it starts to forward frames. In addition, each port needs time to listen for conflicting information that would make it return to a discarding state; otherwise, temporary data loops might result.

•Designated Root – The priority and MAC address of the device in the Spanning Tree that this switch has accepted as the root device.

-Root Port – The number of the port on this switch that is closest to the root. This switch communicates with the root device through this port. If there is no root port, then this switch has been accepted as the root device of the Spanning Tree network.

-Root Path Cost – The path cost from the root port on this switch to the root device.

•Configuration Changes – The number of times the Spanning Tree has been reconfigured.

•Last Topology Change – Time since the Spanning Tree was last reconfigured.

These additional parameters are only displayed for the CLI:

•Spanning tree mode – Specifies the type of spanning tree used on this switch:

-STP: Spanning Tree Protocol (IEEE 802.1D)

-RSTP: Rapid Spanning Tree (IEEE 802.1w)

-MSTP: Multiple Spanning Tree (IEEE 802.1s)

•Instance – Instance identifier of this spanning tree. (This is always 0 for the CIST.)

•VLANs configuration – VLANs assigned to the CIST.

•Priority – Bridge priority is used in selecting the root device, root port, and designated port. The device with the highest priority (i.e., lower numeric value) becomes the STA root device. However, if all devices have the same priority, the device with the lowest MAC address will then become the root device.

•Root Hello Time – Interval (in seconds) at which this device transmits a configuration message.

•Root Maximum Age – The maximum time (in seconds) this device can wait without receiving a configuration message before attempting to reconfigure. All device ports (except for designated ports) should receive configuration messages at regular intervals. If the root port ages out STA information (provided in the last configuration message), a new root port is selected from among the device ports attached to the network. (References to “ports” in this section means “interfaces,” which includes both ports and trunks.)

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