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Spanning Tree Algorithm Configuration
3-77
If 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 then
initiate negotiations with other bridges to reconfigure the network to reestablish a
valid network topology.
RSTP is designed as a general replacement for the slower, legacy STP. RSTP
achieves must faster reconfiguration (i.e., around one tenth of the time required by
STP) 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, and
retaining the forwarding database for ports insensitive to changes in the tree
structure when reconfiguration occurs.
Displaying Global Settings
You can display a summary of the current bridge STA information that applies to the
entire switch using the STA Information screen.
Field Attributes
• Spanning Tree State – Shows if the switch is enabled to participate in an
STA-compliant network.
• Bridge ID – A unique identifier for this bridge, consisting of the bridge priority
and MAC address (where the address is taken from the switch system).
• Max Age – The maximum time (in seconds) a 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. Any port that ages out STA information (provided in the last
configuration message) becomes the designated port for the attached LAN. If it
is a root port, a 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.