Owner's Manual

31
STP
The Spanning Tree Algorithm (STA) can be used to detect and disable network loops, and to
provide backup links between Switches. This allows the Switch to interact with other bridging
devices in your network to ensure that only one route exists between any two stations on the
network and provide backup links which automatically take over when a primary link goes down.
STP provides a tree topology for the Switch. There are different types of Spanning tree versions,
including Multiple Spanning Tree Protocol (MSTP) IEEE 802.1w, and Rapid Spanning Tree
Protocol (RSTP) IEEE 802.1s. Please note that only one spanning tree protocol can be activated
on the Switch at a time.
Global Settings
Spanning Tree Protocol (STP) is a Layer 2 protocol that runs on Switches. Spanning Tree Protocol
(STP) allows you to ensure that you do not create loops when you have redundant paths in the
network. STP provides a single active path between two devices on a network in order to prevent
loops from being formed when the Switch is interconnected via multiple paths.
STP uses a distributed algorithm to select a bridging device that serves as the root for the
spanning tree network. By selecting a root port on each bridging device, it can incur the lowest
path cost when forwarding a packet from that device to the root device. It then selects a
designated bridging device from each LAN which incurs the lowest path cost when forwarding a
packet from that LAN to the root device. Next, all ports connected to designated bridging devices
are assigned as designated ports. After determining the lowest cost spanning tree, it enables all
root ports and designated ports, disabling all other ports. Network packets are therefore only
forwarded between root ports and designated ports, eliminating any possible network loops. STP
provides a single active path between two devices on a network in order to prevent loops from
being formed when the Switch is interconnected via multiple paths.
Once a stable network topology has been established, all bridges listen for Hello Bridge Protocol
Data
Units (BPDUs) transmitted from the Root Bridge of the Spanning Tree. If a bridge does not receive
a Hello BPDU after a predefined interval (known as the Maximum Age), the bridge will assume that
the link to the Root Bridge is down and unavailable. This bridge then initiates negotiations with
other bridges to reconfigure the network to reestablish a valid network topology.
Loops occur when alternate routes exist between hosts. Loops in an extended network can cause
the Switch to forward traffic indefinitely, resulting in increased traffic and reducing network
efficiency. Once the STP is enabled and configured, primary links are established and duplicated
links are blocked automatically. The reactivation of the blocked links is also accomplished
automatically.
STP provides a tree topology and other Spanning tree versions supported include STP, Multiple
Spanning Tree Protocol (MSTP), and Rapid Spanning Tree Protocol (RSTP). Please note that only
one spanning tree can be active on the Switch at a time. The default setting is: MSTP.