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DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
62 Switch Management and Operating Concepts
which the packet is transmitted will receive the BPDU. BPDUs
are not directly forwarded by the switch, but the receiving
switch uses the information in the frame to calculate a BPDU,
and, if the topology changes, initiates a BPDU transmission.
The communication between switches via BPDUs results in the
following:
• One switch is elected as the root switch
• 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.