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

Rapid Spanning Tree

1.2.3 Spanning Tree Priority Vector

To assign roles to the ports, the RSTP bridges exchange configuration infor-
mation between themselves. This information is known as a "Spanning Tree
Priority Vector". It contains the following
D
Bridge identification of the root bridge
D
Root path costs of the transmitting bridge
D
Bridge identification of the transmitting bridge
D
Port identification of the port through which the message was sent
D
Port identification of the port through which the message was received
Based on this information, the bridges involved in the RSTP are capable of
calculating port roles by themselves and defining the port status of their own
ports.

1.2.4 Fast reconfiguration

Why can RSTP react faster than STP to an interruption of the root path?
D
Introduction of edge ports
When reconfiguring RSTP switches to forwarding mode after after the ex-
piration of three seconds
"Hello Time" to be sure, that no BPDU sending bridge is connected.
If the user is sure, that an DTE is connected to this port and still remains,
he can switch off RSTP on this port. Thus there will be no latency at this
port in the case of reconfiguration.
D
Introduction of alternate ports
Since the port roles are already distributed in regular operation, a bridge
can switch over immediately from the root port to the alternative port after
having lost the connection to the root bridge.
D
Communicating with neighboring bridges (point-to-point connections)
The decentralized, direct communication between neighboring bridges
permits immediate reaction to changes in state of the Spanning Tree ar-
chitecture.
Redundancy L3P
Release 3.0 01/07
1.2 The Rapid Spanning Tree Protocol
(see Table 4 on page 35). RSTP waits then for
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