Hirschmann GREYHOUND GRS1020, Справочное руководство

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Redundancy
12.4 The Rapid Spanning Tree Protocol
169
UM Config GRS
Release 8.0 09/2019

Learning: Address learning active (FDB), no data traffic apart from STP-BPDUs

Forwarding: Address learning active (FDB), sending and receiving of every packet type (not only
STP-BPDUs)
12.4.3 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.
12.4.4 Fast reconfiguration
Why can RSTP react faster than STP to an interruption of the root path?

Introduction of edge-ports:
During a reconfiguration, RSTP sets an edge port into the transmission mode after 3 seconds
(default setting). To ascertain that no bridge sending BPDUs is connected, RSTP waits for the
“Hello Time” to elapse.
When the user verifies that an end device is and remains connected to this port, there are no
waiting times 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 alternate 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.

Address table:
With STP, the age of the entries in the FDB determines the updating of communication. RSTP
immediately deletes the entries in those ports affected by a reconfiguration.

Reaction to events:
Without having to adhere to any time specifications, RSTP immediately reacts to events such
as connection interruptions, connection reinstatements, etc.
Note: Data packages could be duplicated and/or arrive at the recipient in the wrong order during
the reconfiguration phase of the RSTP topology. You may also use the Spanning Tree Protocol or
select another redundancy procedure described in this manual.
12.4.5 STP compatibility mode
The STP compatibility mode lets you operate RSTP devices in networks with old installations. If an
RSTP device detects an older STP device, then it switches on the STP compatibility mode on the
relevant port.