Spanning Tree Overview
Configuring Spanning Tree Parameters
page 6-10
OmniSwitch AOS Release 7 Network Configuration Guide
June 2013
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
configuration. If a device connected to Switch A sends broadcast packets, Switch A floods the packets out
all of its active ports. The switches connected to Switch A in turn floods the broadcast packets out their
active ports, and Switch A eventually receives the same packets back and the cycle starts 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 the Spanning Tree
transitions 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
monitoring of links to the new switch.
Switch B
Switch A
Switch D
Switch C