Moxa Technologies EDS-508 user manual How STP Works, STP Requirements

EDS-508 Series User’s Manual Featured Functions

Bridge A

LAN 1

Bridge B

LAN 2

Bridge C

LAN 3

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.

Bridge A

LAN 1

Bridge B

LAN 2

Bridge C

LAN 3

STP determines which path between each bridged segment is the most efficient, and assigns a specific reference point on the network. Once the most efficient path has been determined, all other paths are blocked. Therefore, in the above 3 figures, STP initially determined that the path through Bridge C was the most efficient, and consequently 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 it can configure the network, the STP system requires:

#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

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