Hirschmann GREYHOUND GRS1020, Справочное руководство

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Redundancy
12.3 Spanning Tree
159
UM Config GRS
Release 8.0 09/2019
12.3.1 Basics
Because RSTP is a further development of the STP, every of the following descriptions of the STP
also apply to RSTP.
The tasks of the STP
The Spanning Tree Algorithm reduces network topologies built with bridges and containing ring
structures due to redundant links to a tree structure. In doing so, STP opens ring structures
according to preset rules by deactivating redundant paths. When a path is interrupted because a
network component becomes inoperable, STP reactivates the previously deactivated path again.
This lets redundant links increase the availability of communication.
STP determines a bridge that represents the STP tree structure‘s base. This bridge is called root
bridge.
Features of the STP algorithm:

automatic reconfiguration of the tree structure in the case of a bridge becoming inoperable or
the interruption of a data path

the tree structure is stabilized up to the maximum network size,

stabilization of the topology within a short time period

topology can be specified and reproduced by the administrator

transparency for the end devices

low network load relative to the available transmission capacity due to the tree structure created
Bridge parameters
In the context of Spanning Tree, each bridge and its connections are uniquely described by the
following parameters:

Bridge Identifier

Root Path Cost for the bridge ports,

Port Identifier
Bridge Identifier
The Bridge Identifier consists of 8 bytes. The 2 highest-value bytes are the priority. When
configuring the network, the Management Administrator can change the default setting for the
priority number which is 32768 . The 6 lowest-value bytes of the bridge identifier are the bridge’s
MAC address. The MAC address lets each bridge have unique bridge identifiers.
The bridge with the smallest number for the bridge identifier has the highest priority.
Figure 31: Bridge Identifier, Example (values in hexadecimal notation)
MAC Address Priority
LSB MSB
80 80 00 00 63 51 74 00