Huawei Quidway S6500 Series Operation Manual page 432

Operation Manual - STP
Quidway S6500 Series Ethernet Switches
Upstream sw itch Upstream sw itch
Designated port Designated port
change to change to
Forw arding state Forw arding state
Figure 4-2 MSTP rapid transition
Limitation on the combination of RSTP and MSTP exists when you implement rapid
transition. One example is, with the upstream switch having RSTP employed, the
downstream switch having MSTP employed, and the downstream switch not
supporting RSTP compatible mode, the root port on the downstream switch cannot
receive agreement packets from the upstream switch. So the root port does not send
agreement packets to the upstream switch. As a result, rapid transition fails on the
designated port of the upstream switch, and the port can only change to Forwarding
state after a period two times of the Forward Delay.
As switches of certain manufacturers coming with some proprietary protocols
concerning STP employed, the way to implement rapid transition on the designated
ports of this kind of switches is similar to that of RSTP. So, when a switch of this kind
operates as the upstream switch with Quidway series switches running MSTP
connected to it, the upstream designated port fails to change their state rapidly.
Rapid transition is developed for Quidway series switches to avoid this. When Quidway
series switches with MSTP employed are connected to switches of certain
manufacturers, you can enable rapid transition on the ports of the Quidway series
switches operating as the downstream switches. Among these ports, those operating
as the root ports will then send agreement packets to their upstream ports after they
receive proposal packets from the upstream designated ports rather than wait for the
agreement packets sourced from the upstream switch. This enables designated ports
of the upstream switch to change their states rapidly.
4.2 Rapid Transition Configuration
4.2.1 Prerequisites
As Figure 4-3 shows, a Quidway series switch is connected to a switch coming from
certain manufacturer. The Quidway switch operates as the downstream switch, and the
other operates as the upstream switch. The network operates properly.
Send proposal packets Send proposal packets
to request rapid transition to request rapid transition
Send agreement packets Send agreement packets
Send agreement packets Send agreement packets
Huawei Technologies Proprietary
4-2
Chapter 4 The Rapid Transition Feature
Dow nstream switch Dow nstream switch
Root port blocks Root port blocks
other non-border ports other non-border ports
Root port changes to Root port changes to
Forw arding state and Forw arding state and
sends agreement packets sends agreement packets
to upstream switch to upstream switch
Root port Root port
Designated port Designated port