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Spanning Tree Algorithm Configuration
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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.)