Spanning Tree Algorithm Configuration3-77If a bridge does not get a Hello BPDU after a predefined interval (Maximum Age),the bridge assumes that the link to the Root Bridge is down. This bridge will theninitiate negotiations with other bridges to reconfigure the network to reestablish avalid network topology.RSTP is designed as a general replacement for the slower, legacy STP. RSTPachieves must faster reconfiguration (i.e., around one tenth of the time required bySTP) by reducing the number of state changes before active ports start learning,predefining an alternate route that can be used when a node or port fails, andretaining the forwarding database for ports insensitive to changes in the treestructure when reconfiguration occurs.Displaying Global SettingsYou can display a summary of the current bridge STA information that applies to theentire switch using the STA Information screen.Field Attributes• Spanning Tree State – Shows if the switch is enabled to participate in anSTA-compliant network.• Bridge ID – A unique identifier for this bridge, consisting of the bridge priorityand MAC address (where the address is taken from the switch system).• Max Age – The maximum time (in seconds) a device can wait without receivinga configuration message before attempting to reconfigure. All device ports(except for designated ports) should receive configuration messages at regularintervals. Any port that ages out STA information (provided in the lastconfiguration message) becomes the designated port for the attached LAN. If itis a root port, a new root port is selected from among the device ports attachedto the network. (References to “ports” in this section mean “interfaces,” whichincludes both ports and trunks.)• Hello Time – Interval (in seconds) at which the root device transmits aconfiguration message.• Forward Delay – The maximum time (in seconds) the root device will waitbefore changing states (i.e., discarding to learning to forwarding). This delay isrequired because every device must receive information about topologychanges before it starts to forward frames. In addition, each port needs time tolisten 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 SpanningTree 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 noroot port, then this switch has been accepted as the root device of theSpanning Tree network.- Root Path Cost – The path cost from the root port on this switch to the rootdevice.
