Chapter 4: Web configuration
NS3562-8P-2S-V2 Industrial Managed Switch User Manual
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The IEEE 802.1D Spanning Tree Protocol and IEEE 802.1w Rapid Spanning Tree
Protocol allow for the blocking of links between switches that form loops within the
network. When multiple links between switches are detected, a primary link is
established. Duplicated links are blocked from use and become standby links. The
protocol allows for the duplicate links to be used in the event of a failure of the primary
link. Once the STP is configured and enabled, primary links are established and
duplicated links are blocked automatically. The reactivation of the blocked links (at the
time of a primary link failure) is also accomplished automatically without operator
intervention.
This automatic network reconfiguration provides maximum uptime to network users.
However, the concepts of the spanning tree algorithm and protocol are a complicated
and complex subject and must be fully researched and understood. It is possible to
cause serious degradation of the performance of the network if the spanning tree is
incorrectly configured. Please read the following before making any changes from the
default values.
The switch STP performs the following functions:
• Creates a single spanning tree from any combination of switching or bridging
elements.
• Creates multiple spanning trees from any combination of ports contained within a
single switch, in user specified groups.
• Automatically reconfigures the spanning tree to compensate for the failure, addition,
or removal of any element in the tree.
• Reconfigures the spanning tree without operator intervention.
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: