Hirschmann MACH 1040 Series, User Manual

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Spanning Tree
Redundancy L2B
Release 6.0 07/2010
4.6 The Rapid Spanning Tree
Protocol
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Based on this information, the bridges participating in RSTP are able to
determine port roles autonomously and define their local ports’ states.
4.6.4 Fast reconfiguration
Why can RSTP react faster than STP to an interruption of the root path?
X
Introduction of edge ports:
During a reconfiguration, RSTP sets an edge port to the transmission
mode after 3 seconds and then waits for the “Hello Time”
(see table 8) to
elapse, to ascertainthat no BPDU-sending bridge is connected.
When the user ascertains 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.
X
Introduction of alternate ports:
As the port roles are already determined 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.
X Communication with neighboring bridges (point-to-point connections):
The decentralized, direct communication between neighboring bridges
enables immediate reaction to status changes in the spanning tree
architecture.
X
Address table:
With STP, the age of the entries in the address table determines the
updating of the communication. RSTP immediately deletes the entries for
those ports affected by a reconfiguration.
X Reaction to events:
Without having to adhere to any time specifications, RSTP immediately
reacts to events such as connection interruptions, connection
reinstatements, and the like.