l
STP port roles
–
Root port
The root port is the port that is nearest to the root bridge. The root port is determined
based on the path cost. Among all the STP-capable ports on the network bridge, the port
with the lowest root path cost is the root port. There is only one root port on an STP-
capable device, but there is no root port on the root bridge.
–
Designated Port
The designated port on a switching device forwards bridge protocol data units (BPDUs)
to the downstream switching device. All ports on the root bridge are designated ports.
A designated port is selected for each network segment. The device on which the
designated port resides is called the designated bridge.
l
RSTP port roles
Compared with STP, RSTP has two additional types of ports, the alternate port and backup
port. More port roles are defined to simplify deployment of STP.
Figure 7-1
Diagram of port roles
S2
S3
A
A
B
A
a
S2
S3
A
A
B
A
a
B
b
Huawei AR3200 Series Enterprise Routers
Configuration Guide - LAN
7 STP/RSTP Configuration
Issue 02 (2012-03-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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