User`s manual

NPort S8000 Series Switch Featured Functions
6-15
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 determined that traffic from LAN segment 2 to LAN segment 1 should flow through
Bridges C and A because this path has a greater bandwidth and is therefore more efficient.
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.
Bridge B
Bridge C
LAN 1
LAN 2
LAN 3
Bridge A
Bridge B
Bridge C
LAN 1
LAN 2
LAN 3
Bridge A
Bridge B
Bridge C
LAN 1
LAN 2
LAN 3
Bridge A