24-port NWay Ethernet Switch User’s Guide
Switch Management and Operating Concepts
45
??
The shortest distance to the root switch is calculated for
each switch
??
A designated switch is selected. This is the switch closest
to the root switch through which packets will be
forwarded to the root.
??
A port for each switch is selected. This is the port
providing the best path from the switch to the root switch.
??
Ports included in the STP are selected.
Creating a Stable STP Topology
If all switches have STP enabled with default settings, the switch
with the lowest MAC address in the network will become the root
switch. By increasing the priority (lowering the priority number)
of the best switch, STP can be forced to select the best switch as
the root switch.
When STP is enabled using the default parameters, the path
between source and destination stations in a switched network
might not be ideal. For instance, connecting higher-speed links
to a port that has a higher number than the current root port
can cause a root-port change. The goal is to make the fastest
link the root port.
STP Port States
The BPDUs take some time to pass through a network. This
propagation delay can result in topology changes where a port
that transitioned directly from a Blocking state to a Forwarding
state could create temporary data loops. Ports must wait for
new network topology information to propagate throughout the
network before starting to forward packets. They must also wait
