Gigabit Ethernet Switch User’s Guide
Switch Management
23
Spanning Tree Algorithm
The Spanning Tree Algorithm (STA) in the Switch allows you to
create alternative paths (with multiple switches or other types of
bridges) in your network. These backup paths are idle until the
Switch determines that a problem has developed in the primary
paths. When a primary path is lost, the switch providing the
alternative path will automatically go into service with no operator
intervention. This automatic network reconfiguration provides
maximum uptime to network users. The concept of the Spanning
Tree Algorithm is a complicated and complex subject and must be
fully researched and understood. Please read the following before
making any changes.
♦
Network loop detection and prevention
With STA,
there will be only one path between any two LANs. If there
is more than one path, forwarded packets will loop
indefinitely. STA detects any looped path and selects the
path with the lowest path cost as the active path, while
blocking the other path and using it as the backup path.
♦
Automatic topology re-configuration
When the path
for which there is a backup path fails, the backup path will
be automatically activated, and STA will automatically re-
configure the network topology.
STA Operation Levels
STA operates on two levels: the bridge level and the port level. On
the bridge level, STA calculates the Bridge Identifier for each
Switch, then sets the Root Bridge and the Designated Bridges. On
the port level, STA sets the Root Port and Designated Ports.
Details are as follows: