The Rapid Spanning Tree Protocol; Port Roles - Hirschmann RS20 User Manual

Spanning Tree
4.6 The Rapid Spanning Tree
Protocol
The RSTP uses the same algorithm for determining the tree structure as
STP. RSTP merely changes parameters, and adds new parameters and
mechanism that speed up the reconfiguration if a link or bridge becomes
inoperable.
The ports play a significant role in this context.
4.6.1

Port roles

RSTP assigns each bridge port one of the following roles
Root port
This is the port on which a bridge receives data packets with the lowest
path costs from the root bridge.
If there is more than 1 port with the same low path costs, the bridge
identifier determines which port is the root port.
If there is more than 1 port with the same low path costs connected to the
same bridge, the port identifier determines which port is the root port
fig. 17).
The root bridge itself does not have a root port.
Designated port
The bridge in a network segment that has the lowest root path costs is the
designated bridge. If more than 1 bridge has the same root path costs, the
bridge with the smallest value bridge identifier becomes the designated
bridge. The port on this bridge that connects it to a network segment
leading to the root bridge, is the designated port.
Redundancy L2B
Release 6.0 07/2010
4.6 The Rapid Spanning Tree
(see fig.
Protocol
21):
(see
53