Moxa Technologies 405A SERIES User Manual

 

 

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 determines 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 following sections. 

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. 

y  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 is 32768.