Huawei AR530 Series, Руководство по настройке

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Table 6-3 Four important fields
Field Description
Root ID Each STP network has only one root bridge.
Root path cost The distance between the port sending the configuration
BPDU and the root bridge determines the path cost to
the root bridge.
Sender BID It is the BID of the device that sends the configuration
BPDU.
PID It is the PID of the port that sends the configuration
BPDU.
After a device on the STP network receives a configuration BPDU, it compares the fields listed
in
Table 6-3 with its own values. The four comparison principles are as follows:
NOTE
During STP calculation, all factors follow the rule of "the smaller the value, the higher the priority."
l Smallest BID: used to select the root bridge. Devices on an STP network select the device
with the smallest BID based on the root ID field in
Table 6-3 .
l Smallest root path cost: used to select the root port on a non-root bridge. On the root bridge,
the path cost of each port is 0.
l Smallest sender BID: used to select the root port among ports with the same root path cost.
The port with the smallest BID is selected as the root port in STP calculation. For example,
S2 has a smaller BID than S3 in
Figure 6-2 . If the BPDUs received on port A and port B
of S4 contain the same root path cost, port B becomes the root port on S4 because the BPDU
received on port B has a smaller sender BID.
l Smallest PID: used to determine which port should be blocked when multiple ports have
the same root path cost. The port with the greatest PID is blocked. The PIDs are compared
in the scenario shown in
Figure 6-4 . The BPDUs received on port A and port B of S1
contain the same root path cost and sender BID. Port A has a smaller PID than port B.
Therefore, port B is blocked to prevent loops.
Huawei AR530&AR550 Series Industrial Switch Routers
Configuration Guide - Ethernet Switching
6 STP/RSTP Configuration
Issue 01 (2014-11-30) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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