User`s manual

EDS-516A Series User’s Manual Featured Functions
3-27
Coupling Mode
Setting Description Factory Default
Dual Homing
Select this item to change to the
Dual Homing configuration page
Primary Port: port 13
Backup Port: port 14
Ring Coupling
(backup)
Select this item to change to the
Ring Coupling (backup)
configuration page
Coupling Port: port 13
Ring Coupling
(primary)
Select this item to change to the
Ring Coupling (primary)
configuration page
Coupling Port: port 13
Primary/Backup Port
Setting Description Factory Default
Primary Port
Select any port of the EDS-516A to
be the primary port.
port 13
Backup Port
Select any port of the EDS-516A to
be the backup port.
port 14
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 EDS-516A’s STP feature is disabled by
default. To be completely effective, you must enable RSTP/STP on every EDS-516A 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:
y The topology of a bridged network will be determined much more quickly compared to STP.
y RSTP is backward compatible with STP, making it relatively easy to deploy. For example:
¾ Defaults to sending 802.1D style BPDUs if packets with this format are received.
¾ STP (802.1D) and RSTP (802.1W) can operate on different ports of the same EDS-516A.
This feature is particularly helpful when the EDS-516A’s 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:
y Locate and then disable less efficient paths (i.e., paths that have a lower bandwidth).
y 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.