Switch Administration Guide

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Technical Documentation > Switch Administration Guide > System Management > Switching > Spanning Tree Protocol > Global Settings

Global Settings

Global settings are available under Spanning Tree Protocol Settings Tab. The Root Bridge serves as an administrative point for all Spanning Tree calculations to determine which redundant links to block in order to prevent network loops.

All other decisions in a spanning tree network, such as ports being blocked and ports being put in a forwarding mode, are made regarding a root bridge. The root bridge is the “root” of the constructed “tree” within a spanning tree network. Thus, the root bridge is the bridge with the lowest bridge ID in the spanning tree network. The bridge ID includes two parts; the bridge priority (2 bytes) and the bridge MAC address (6 bytes). The 802.1d default bridge priority is: 32768. STP devices exchange Bridge Protocol Data Units (BPDUs) periodically. All bridges “listen” for Hello BPDUs (Bridge Protocol Data Units) transmitted from the root bridge. If a bridge does not get a Hello BPDU after a predefined interval (called the Maximum Age), the bridge assumes that the link to the root bridge is down. The bridge then initiates negotiations with other bridges to reconfigure the network to re-establish a valid network topology.

Name	This name uniquely identifies the MSTI (Multiple Spanning Tree Instance). Enter a descriptive name (up to 32 characters) for an MST region. The default is the MAC address name of the device running MSTP.
Revision	Displays the Spanning Tree Configuration Revision. Default revision is 0. Decimal values cannot be configured.
Hello Time	Displays the Switch Hello Time. This is the amount of time between each bridge protocol data unit sent on a port. The default is 2 seconds.
Forward Time	Displays the Switch Forward Delay Time. This is the time (in seconds) the Root Switch will wait before changing states (called listening to learning).
Max Age	Displays the bridge Switch Maximum Age Time. This is the amount of time a bridge waits before sending a configuration message. The default is 20 seconds. Ensure to calculate the Max Age using 2(ForwardDelay -1)>=MaxAge >= 2(Hello Time + 1).
Max Hops	Displays the BPDU Hop count. The max hop count is the maximum number of hops the BPDU can traverse before getting discarded and also before the information held for a port is aged out. The default count is 10.

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