User`s manual

IKS-6726 Featured Functions
3-30
You get essentially the same functionality with RSTP and STP. To see how the two systems different, please
refer to Differences between RSTP and STP later in this chapter.
NOTE The STP protocol is part of the IEEE Std 802.1D, 1998 Edition bridge specification. The explanation given
below uses bridge instead of switch.
What is STP?
STP (802.1D) is a bridge-based system that is used to implement parallel paths for network traffic. STP uses a
loop-detection process to:
• Locate and then disable less efficient paths (i.e., paths that have a lower bandwidth)
• Enable one of the less efficient paths if the most efficient path fails
The figure below shows a network made up of three LANs separated by three bridges. Each segment uses at
most two paths to communicate with the other segments. Since this configuration can give rise to loops, the
network will overload if STP is not enabled.
If STP is enabled, it will detect duplicate paths and prevent, or block, one of them from forwarding traffic. In the
following example, STP determined that traffic from LAN segment 2 to LAN segment 1 should flow through
Bridges C and A because this path has a greater bandwidth and is therefore more efficient.
What happens if a link failure is detected? As shown in next figure, the STP process reconfigures the network
so that traffic from LAN segment 2 flows through Bridge B.