Chapter 4 The Rapid Transition Feature; Introduction - Huawei Quidway S6500 Series Operation Manual

Operation Manual - STP
Quidway S6500 Series Ethernet Switches

Chapter 4 The Rapid Transition Feature

4.1 Introduction

Designated ports with RSTP (rapid spanning tree protocol) or MSTP (multiple spanning
tree protocol) employed use the following two types of packets to implement rapid
transition:
Proposal packets: Packets sent by designated ports requesting rapid transition
Agreement packets: Packets used to acknowledge rapid transition requests
The designated port of an upstream switch with RSTP or MSTP employed can perform
rapid transition operation only after the port receives agreement packets from the
downstream switch. Switches with different protocols among RSTP and MSTP
employed act differently as follows:
As for switches with MSTP employed, a downstream switch sends agreement
packets to the upstream switch only after it receive agreement packets from the
upstream switch. That is, the upstream switch sends agreement packets to the
downstream switch.
As for switches with RSTP employed, the upstream switch does not send
agreement packets to the downstream switch.
Figure 4-1 and Figure 4-2 illustrate the RSTP and MSTP rapid transition mechanisms.
Upstream sw itch Upstream sw itch
Designated port Designated port
changes to changes to
Forw arding state Forw arding state
Figure 4-1 RSTP rapid transition
Sends proposal packets to Sends proposal packets to
request rapid transition request rapid transition
Sends agreement packets Sends agreement packets
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4-1
Chapter 4 The Rapid Transition Feature
Dow nstream switch Dow nstream switch
Root port blocks other Root port blocks other
non-border ports, non-border ports,
changes to Forwarding changes to Forwarding
state, and sends state, and sends
agreement packets agreement packets
to the upstream switch to the upstream switch
Root port Root port
Designated port Designated port