Stp - EnGenius EWS Series User Manual

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,
supported, including Spanning Tree Protocol (STP) IEEE 802.1D, Multiple Spanning Tree Protocol (MSTP)
IEEE 802.1w, and Rapid Spanning Tree Protocol (RSTP) IEEE 802.1s. Please note that only one spanning
tree can be active 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. It does this by selecting a root port on each bridging device to 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.
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