84 Spanning Tree Concepts ELS100-24TXM
Spanning Tree Protocol Operation
When the Spanning Tree Protocol is enabled for the first time or when
there is a change in the network topology, such as a failure or the addition
or removal of a component, the Spanning Tree Protocol automatically
sets up the active topology of the current network.

Communicating Between Bridges

Periodically, all devices running the Spanning Tree Protocol on a networ k
transmit packets to each other “in care of” the Bridge Grou p Address
which all bridges share. When a bridge receives a frame sent to the
Bridge Group Address, the bridge’s Spanning Tree Protocol processes
the packet. Application software and other LAN segments ignore the
packet. 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 bri dges
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. Wher e a
duplicate path exists, the non-designated port is put into a blocking state.

Remapping Network Topology

If there is a change in the network topology due to a failure or the removal
or addition of any active components, the active topology also changes.
This may trigger a change in the state of some blocked ports.