Spanning Tree Priority Vector; Fast Reconfiguration - Hirschmann RS20 User Manual

Spanning Tree
6.6.3

Spanning Tree Priority Vector

To assign roles to the ports, the RSTP bridges exchange configuration
information with each other. This information is known as the Spanning Tree
Priority Vector. It is part of the RSTP BPDUs and contains the following
information:
 Bridge identification of the root bridge
 Root path costs of the sending bridge

Bridge identification of the sending bridge
 Port identifiers of the ports through which the message was sent
 Port identifiers of the ports through which the message was received
Based on this information, the bridges participating in RSTP are able to
determine port roles themselves and define the port states of their own ports.
6.6.4

Fast reconfiguration

Why can RSTP react faster than STP to an interruption of the root path?
 Introduction of edge-ports:
During a reconfiguration, RSTP switches an edge port into the
transmission mode after three seconds and then waits for the "Hello Time"
(see table 15)
connected.
When the user determines that a terminal device is connected at this port
and will remain connected, he can switch off RSTP at this port. Thus no
waiting times occur at this port in the case of a reconfiguration.

Introduction of alternate ports:
As the port roles are already distributed in normal operation, a bridge can
immediately switch from the root port to the alternative port after the
connection to the root bridge is lost.
 Communication with neighboring bridges (point-to-point connections):
Decentralized, direct communication between neighboring bridges
enables reaction without wait periods to status changes in the spanning
tree topology.
106
to elapse, to be sure that no bridge sending BPDUs is
6.6 The Rapid Spanning Tree
UM RedundConfig L2P
Release 8.0 05/2013
Protocol