Fast Transition; Introduction - 3Com 8807 Configuration Manual

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Introduction

F T
AST RANSITION
The designated port fast transition mechanism of RSTP and MSTP uses two types
of protocol packets:
proposal packet: Requests for fast transition.
■
agreement packet: Permits the opposite end to perform fast state transition.
■
RSTP and MSTP request that a designated port of the upstream switch can
perform fast transition after receiving the agreement packet from the downstream
switch. RSTP and MSTP are different in the following:
For MSTP, the upstream switch sends the agreement packet to the downstream
■
switch first. After receiving the agreement packet, the downstream switch
sends the agreement packet to the upstream switch.
For RSTP, the upstream switch does not send the agreement packet to the
■
downstream switch.
Figure 33 and Figure 34 show the designated port fast transition mechanisms of
RSTP and MSTP.
Figure 33 Designated port fast transition mechanism of RSTP
Upstream switch Upstream switch
Send the proposal message to Send the proposal message to
request for fast transition request for fast transition
Send the agreement message Send the agreement message
The designated The designated
port enters the port enters the
forwarding state forwarding state
Downstream switch Downstream switch
The root port congests other The root port congests other
non-edge ports and enters the non-edge ports and enters the
forwarding state, and then forwarding state, and then
Forwards the agreement Forwards the agreement
message to the upstream switch message to the upstream switch
Root port Root port
Designated port Designated port