Bridge Protocol Data Units - D-Link DES-3326 User Manual

24-port NWay Ethernet Switch User's Guide
Table 5-2. STP Parameters – Port Group Level

Bridge Protocol Data Units

For STP to arrive at a stable network topology, the following
information is used:
The unique switch identifier
The path cost to the root associated with each switch port
The port identifier
STP communicates between switches on the network using
Bridge Protocol Data Units (BPDUs). Each BPDU contains the
following information:
The unique identifier of the switch that the transmitting
switch currently believes is the root switch
The path cost to the root from the transmitting port
The port identifier of the transmitting port
The switch sends BPDUs to communicate and construct the
spanning-tree topology. All switches connected to the LAN on
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
44 Switch Management and Operating Concepts