Hirschmann MACH 1040 Series, User Manual

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Spanning Tree
46
4.2 Rules for Creating the Tree Struc-
ture
Redundancy
Release 6.0 07/2010
4.2 Rules for Creating the Tree
Structure
4.2.1 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
X bridge identifier,
X
root path cost and
X port identifier
(see IEEE 802.1D).
4.2.2 Setting up the tree structure
X 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.
X The structure of the tree depends on the root path costs. STP selects the
structure so that the path costs between each individual bridge and the
root bridge become as small as possible.
X If more than 1 path exists with the same root path costs, the priority of the
bridge identifier for the bridge connected to one of these paths decides
which bridge should block.