Spanning Tree Overview; Spanning Tree Protocol (Ieee 802.1D) - Symbol ES3000 Manual

5-2 ES3000 Advanced Concept Guide

5.1 Spanning Tree Overview

The ES2000 switch can be configured to use one of three spanning tree protocols. Spanning Tree
Protocol (STP) is compatible with legacy equipment. Rapid Spanning Tree Protocol (RSTP) is
significantly faster than STP. Multiple Spanning Tree Protocol (MSTP) is based on RSTP and extends
RSTP in a way that is useful for switches implementing VLANs.

5.2 Spanning Tree Protocol (IEEE 802.1D)

The Spanning Tree Protocol (STP) ensures that no loops are formed in a meshed network while
providing a path between any two nodes in the network. STP finds non-looping paths between
stations by requiring switches to exchange messages called bridge protocol data units (BPDU). BPDUs
contain information about the switch and its connections to other switches.
For each VLAN, the STP process selects a root switch. If the switches differ in priority, the root switch
is the switch with the highest priority. If all switches are of equal priority, the root switch is the switch
with the lowest MAC address. It is usually best for the root switch to be the switch which has the
fastest connection to the outside world. The network administrator can force this switch to be the
root switch by assigning it the highest priority (lowest numerical value).
After a root switch has been chosen, a single path is chosen from that switch to all other switches,
disabling or blocking the other paths. If there are multiple paths to another switch, it will first choose
the path to the highest-priority switch. If all switches have the same priority, it will choose the path
with the lowest cost. If all paths have the same cost, it will choose the path to the lowest MAC
address.
The port which connects a non-root switch to the root switch, directly or indirectly, is known the root
port for that switch. A switch which is used as the connection between the root switch and another
switch is known as the designated switch for the destination switch. The port on a designated switch
which is selected for communication with a non-root switch is known as the designated port for the
destination switch.