Moxa Technologies EDS-518A Series User Manual

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EDS-518A Series User’s Manual

Featured Functions

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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.

STP will determine which path between each bridged segment is most efficient, and then assigns a
specific reference point on the network. When the most efficient path has been identified, the other
paths are blocked. In the previous 3 figures, STP first determined that the path through Bridge C
was the most efficient, and as a result, blocked the path through Bridge B. After the failure of
Bridge C, STP re-evaluated the situation and opened the path through Bridge B.

How STP Works

When enabled, STP determines the most appropriate path for traffic through a network. The way it
does this is outlined in the sections below.

STP Requirements

Before STP can configure the network, the system must satisfy the following requirements:
y

Communication between all the bridges. This communication is carried out using Bridge

Protocol Data Units (BPDUs), which are transmitted in packets with a known multicast
address.

Each bridge must have a Bridge Identifier that specifies which bridge acts as the central

reference point, or Root Bridge, for the STP system—bridges with a lower Bridge Identifier
are more likely to be designated as the Root Bridge. The Bridge Identifier is calculated using
the MAC address of the bridge and a priority defined for the bridge. The default priority of
EDS-518A is 32768.

Bridge B

Bridge C

LAN 1

LAN 2

LAN 3

Bridge A