Moxa Technologies Moxa EtherDevice Switch EDS-508 - Manual (Page 40)

EDS-508 Series User’s Manual Featured Functions
3-24
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 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
Bridge B
Bridge C
LAN 1
LAN 2
LAN 3
Bridge A
Bridge B
Bridge C
LAN 1
LAN 2
LAN 3
Bridge A