Port Role - Huawei AR530 series Configuration Manual

Huawei AR530&AR550 Series Industrial Switch Routers
Configuration Guide - Ethernet Switching
CIST
A CIST, calculated by using STP or RSTP, connects all the switching devices on a switching
network.
As shown in
SST
A Single Spanning Tree (SST) is formed in either of the following situations:
l
l
As shown in

Port Role

Based on RSTP, MSTP has two additional port types. MSTP ports can be root ports, designated
ports, alternate ports, backup ports, edge ports, master ports, and regional edge port.
The functions of root ports, designated ports, alternate ports, and backup ports have been defined
in RSTP.
Table 7-2 Port roles
Port
Role
Root port
Designate
d port
Alternate
port
Issue 01 (2014-11-30)
Figure 7-6, the ISTs and the CST form a complete spanning tree, the CIST.
A switching device running STP or RSTP belongs to only one spanning tree.
An MST region has only one switching device.
Figure 7-6, the switching device in B0 forms an SST.
Table 7-2 lists all port roles in MSTP.
NOTE
Except edge ports, all ports participate in MSTP calculation.
A port can play different roles in different spanning tree instances.
Description
A root port is the non-root bridge port closest to the root bridge. Root bridges do
not have root ports.
Root ports are responsible for sending data to root bridges.
As shown in
root port on S2.
The designated port on a switching device forwards BPDUs to the downstream
switching device.
As shown in
designated port on S3.
l From the perspective of sending BPDUs, an alternate port is blocked after a
BPDU sent by another bridge is received.
l From the perspective of user traffic, an alternate port provides an alternate
path to the root bridge. This path is different than using the root port.
As shown in
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Figure 7-7, S1 is the root; CP1 is the root port on S3; BP1 is the
Figure 7-7, AP2 and AP3 are designated ports on S1; CP2 is a
Figure 7-7, BP2 is an alternate port.
7 MSTP Configuration
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