Spanning Tree Overview Configuring Spanning Tree Parameters
page 7-10 OmniSwitch 6800/6850/9000 Network Configuration Guide March 2008
Topology Examples
The following diagram shows an example of a physical network topology that incorporates data path
redundancy to ensure fault tolerance. These redundant paths, however, create loops in the network config-
uration. If a device connected to Switch A sends broadcast packets, Switch A will flood the packets out all
of its active ports. The switches connected to Switch A will in turn flood the broadcast packets out their
active ports, and Switch A will eventually receive the same packets back and the cycle will start over
again. This causes severe congestion on the network, often referred to as a broadcast storm.
Physical Topology Example
The Spanning Tree Algorithm prevents network loops by ensuring that there is always only one active link
between any two switches. This is done by transitioning one of the redundant links into a blocking state,
leaving only one link actively forwarding traffic. If the active link goes down, then Spanning Tree will
transition one of the blocked links to the forwarding state to take over for the downed link. If a new switch
is added to the network, the Spanning Tree topology is automatically recalculated to include the monitor-
ing of links to the new switch.
Switch B
Switch A
Switch D
Switch C
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