Allied Telesis AT-S26 - Manual (Page 148)

Spanning Tree Protocol Concepts
148
Spanning Tree Protocol Operation
When STP is enabled for the first time, or when the network topology
changes due to a failure, the addition, or removal of a component,
the spanning tree algorithm automatically sets up the active
topology of the current network.
Communication Between Bridges
Periodically, all devices running STP on a network transmit packets to
each other through the Bridge Group Address which all bridges
share. When a bridge receives a packet sent to the Bridge Group
Address, the bridge’s STP processes the packet. The packet is ignored
by application software and other LAN segments. Bridges
communicate between each other in order to determine the root
bridge.
Selecting a Root Bridge and Designated Bridges
During communication between bridges, one bridge is determined
to have the lowest bridge identifier. This bridge becomes the root
bridge.
After the root bridge has been selected, each LAN segment looks for
the bridge that has the lowest cost relative to the root bridge. These
bridges become designated bridges.
Selecting Designated Ports
Each designated bridge selects a designated port. This port is
responsible for forwarding packets to the root bridge.
Handling Duplicate Paths
When the active topology of the network is determined, all packets
between any two nodes in the network use only one path. Where a
duplicate path exists, the non-designated port is put into a blocking
state.