Moxa Technologies PT-7728 user manual STP/RSTP Concept, What is STP?

PT-7728 User’s Manual Featured Functions

The STP/RSTP Concept

Spanning Tree Protocol (STP) was designed to help reduce link failures in a network and provide protection from loops. Networks that have a complicated architecture are prone to broadcast storms caused by unintended loops in the network. The PT-7728’s STP feature is disabled by default. To be completely effective, you must enable RSTP/STP on every PT-7728 connected to your network.

Rapid Spanning Tree Protocol (RSTP) implements the Spanning Tree Algorithm and Protocol defined by IEEE Std 802.1w-2001. RSTP provides the following benefits:

yThe topology of a bridged network will be determined much more quickly compared to STP.

yRSTP is backward compatible with STP, making it relatively easy to deploy. For example:

¾It defaults to sending 802.1D style BPDUs if packets with this format are received.

¾STP (802.1D) and RSTP (802.1w) can operate on different ports of the same PT-7728. This feature is particularly helpful when PT-7728 ports connect to older equipment, such as legacy switches.

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:

yLocate and then disable less efficient paths (i.e., paths that have a lower bandwidth)

yEnable 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.

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