Creating A Stable Stp Topology - Enterasys VH-2402-L3 Management Manual

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
•
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.
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