Telindus 1031, User And Reference Manual

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Telindus 1031 Router Chapter 8
User manual Configuring the bridge
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8.3 The Spanning Tree root bridge
What is the root bridge?
Spanning Tree defines a tree with a root bridge and a loop-free path from the root to all bridges in the
extended network. The root bridge is the logical centre of the Spanning Tree topology.
Redundant data paths are forced into a stand-by (blocked) state. If a network segment in the spanning
tree fails and a redundant path exists, the spanning-tree algorithm recalculates the spanning-tree topol-
ogy and activates the stand-by path.
How is a root bridge selected?
All bridges in the network participating in Spanning Tree gather information about other bridges in the
network. They do this through an exchange of data messages called Bridge Protocol Data Units
(BPDUs).
This exchange of messages results in the following phases:
Phase Description
1 The selection of a root bridge.
The bridge with the highest bridge priority (i.e. the lowest numerical priority value) is
selected as the root bridge. If all bridges are configured with the default priority (32768),
the bridge with the lowest MAC address becomes the root bridge.
2 The selection of a designated bridge for every bridged LAN segment.
3 The removal of loops in the bridged network by blocking bridge ports connected to redun-
dant links.