Operation Manual – MSTP
H3C S3100 Series Ethernet Switches Chapter 1 MSTP Configuration
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z For MSTP, the upstream switch sends agreement packets to the downstream
switch; and the downstream switch sends agreement packets to the upstream
switch only after it receives agreement packets from the upstream switch.
z For RSTP, the upstream switch does not send agreement packets to the
downstream switch.
Figure 1-6 and Figure 1-7 illustrate the rapid transition mechanisms on designated
ports in RSTP and MSTP.
Figure 1-6 The RSTP rapid transition mechanism
Figure 1-7 The MSTP rapid transition mechanism
The cooperation between MSTP and RSTP is limited in the process of rapid transition.
For example, when the upstream switch adopts RSTP, the downstream switch adopts
MSTP and the downstream switch does not support RSTP-compatible mode, the root
port on the downstream switch receives no agreement packet from the upstream switch
and thus sends no agreement packets to the upstream switch. As a result, the
designated port of the upstream switch fails to transit rapidly and can only turn to the
forwarding state after a period twice the forward delay.
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