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5-12 C
HAPTER
5: A
DVANCED
M
ANAGEMENT
Spanning Tree Protocol
Using the Spanning Tree Protocol (STP) functionality
of your Switch makes your network more fault toler-
ant.
The following sections explain more about STP and
the STP features supported by the Switch.
STP is not currently supported over an Asynchronous
Transfer Mode (ATM) network. Therefore, if you
have an ATM OC-3c Module installed in your
Switch, it does not join the STP system.
What is STP?
STP is a part of the 802.1d bridge specification
defined by the IEEE Computer Society. To explain
STP more effectively, the Switch 1000 will be
defined as a bridge.
STP is a bridge-based system for providing fault tol-
erance on networks. STP allows you to implement
parallel paths for network traffic, and ensure that:
■
Redundant paths are disabled when the main
paths are operational
■
Redundant paths are enabled if the main paths
fail
As an example, Figure 5-10
shows a network con-
taining three LAN segments separated by three
bridges. With this configuration, each segment can
communicate with the others using two paths. This
configuration creates loops which cause the net-
work to overload; however, STP allows you to have
this configuration because it detects duplicate paths
and immediately prevents, or
blocks
, one of them
from forwarding traffic.
Figure 5-11
shows the result of enabling STP on the
bridges in the configuration. The STP system has
decided that traffic from LAN segment 2 to LAN
segment 1 can only flow through Bridges C and A.
If the link through Bridge C fails, as shown in
Figure 5-12
, the STP system reconfigures the net-
work so that traffic from segment 2 flows through
Bridge B.