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C
ONFIGURING
THE
S
WITCH
3-118
When using STP or RSTP, it may be difficult to maintain a stable path
between all VLAN members. Frequent changes in the tree structure can
easily isolate some of the group members. MSTP (an extension of RSTP) is
designed to support independent spanning trees based on VLAN groups.
Once you specify the VLANs to include in a Multiple Spanning Tree
Instance (MSTI), the protocol will automatically build an MSTI tree to
maintain connectivity among each of the VLANs. MSTP maintains contact
with the global network because each instance is treated as an RSTP node
in the Common Spanning Tree (CST).
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.