Rapid Spanning Tree
54
4.2
Rules for creating the tree structure
Redundancy L2E
Release
4.1
03/08
4.2 Rules for creating the tree
structure
4.2.1 Bridge information
To calculate the tree structure, the bridges require 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 costs 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 the root
bridge. It is 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 are kept to a minimum.
X In the case of a number of paths 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.
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