The Rapid Spanning Tree Protocol; Port Roles - Hirschmann PowerMICE User Manual

Rapid Spanning Tree
1.2 The Rapid Spanning Tree
Protocol
RSTP does not change the STP tree structure calculation. RSTP only alters
parameters, adds new parameters and mechanisms that accelerate the re-
configuration in the event of an error.
The ports play a major role within this context.

1.2.1 Port roles

RSTP assigns one of the following roles to each bridge port
D
Root-Port
This is the port at which a bridge receives data packets with the lowest
path costs from the root bridge.
If there are several ports with the same low path costs, the bridge identi-
fication determines which port is the root port.
If there is also more ports with the same low path costs and the same brid-
ge identification, the port identification determines which port is the root
port (see Fig.
The root bridge does not have a root port itself.
D
Designated Port
The bridge in a network segment that has the lowest root bridge costs is
the Designated Bridge. If a number of bridges have the same root bridge
costs, then the bridge with the smallest value for the bridge identification
becomes the designated bridge. The port on this bridge that connects it
to a network segment that leads from the root bridge, is the designated
port.
Redundancy L3P
Release 3.0 01/07
4).

1.2 The Rapid Spanning Tree Protocol

(see Fig. 8):
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