Rapid Spanning Tree
98
6.6
The Rapid Spanning Tree Protocol
Redundanz L2P
Release
5.0
04/09
X Bridge identifier of the root bridges
X Root path costs for the sending bridges
X Bridge identifier for the sending bridges
X Port identifiers of the ports through which the message was sent
X Port identifiers of the ports through which the message was received
Based on this information, the bridges participating in RSTP are able to
calculate 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?
X Introduction of edge ports
During a reconfiguration, RSTP switches an edge port into the trans-
mission mode after three seconds and then waits for the “Hello Time” (see
table 14) to elapse, to be sure that no bridge sending BPDUs is
connected.
When the user is sure 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 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.
X Communication with neighboring bridges (point-to-point connections)
Decentralized, direct communication between neighboring bridges
enables immediate reaction to status changes in the spanning tree
architecture.
X Filter table
With STP, the age of the entries in the filter table determines the updating.
RSTP immediately deletes the entries in 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, etc.
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