S
PANNING

T

REE

A

LGORITHM

12-4

MSTP connects all bridges and LAN segments with a single Common and
Internal Spanning Tree (CIST). The CIST is formed as a result of the
running spanning tree algorithm between switches that su pport the STP,
RSTP, MSTP protocols.
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, the MST Instance ID 0 for the Common Spanning Tree when
spanning tree mode is set to MSTP (page 12-8), 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