Moxa Technologies Moxa EtherDevice Switch EDS-405A - Manual (Page 43)

EDS-408A/405A Series User’s Manual Featured Functions
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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. This
feature is particularly helpful when EDS ports are connected to older equipment, such as
legacy switches.
RSTP provides essentially the same functionality as 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.
If STP is enabled, it will detect duplicate paths and prevent, or block, one of them from forwarding
traffic. In the following example, STP determines that traffic from LAN segment 2 to LAN
segment 1 should flow through Bridges C and A as this path has a greater bandwidth and is
therefore more efficient.
Bridge B
Bridge C
LAN 1
LAN 2
LAN 3
Bridge A