Hirschmann GREYHOUND GRS1020, Reference Manual

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Redundancy
12.3 Spanning Tree
162
UM Config GRS
Release 8.0 09/2019
12.3.2 Rules for Creating the Tree Structure
Bridge information
To determine the tree structure, the bridges need more detailed information about the other bridges
located in the network.
To obtain this information, each bridge sends a BPDU (Bridge Protocol Data Unit) to the other
bridges.
The contents of a BPDU include:

Bridge identifier

Root path costs

Port identifier
(see IEEE 802.1D)
Setting up the tree structure

The bridge with the smallest number for the bridge identifier is called the root bridge. It is (or will
become) the root of the tree structure.

The structure of the tree depends on the root path costs. Spanning Tree selects the structure so
that the path costs between each individual bridge and the root bridge become as small as
possible.