EDS-518A Series User’s Manual

Featured Functions

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:

¾Defaults 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 EDS-518A. This feature is particularly helpful when EDS-518A 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 differ, see the Differences between RSTP and STP section in this chapter.

NOTE

The STP protocol is part of the IEEE Std 802.1D, 1998 Edition bridge specification. The

 

following explanation 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.

LAN 1Bridge B
Bridge A

LAN 2

Bridge C

LAN 3

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.

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