Huawei Quidway S3100 Series Operation Manual page 195

Operation Manual – MSTP
Quidway S3100 Series Ethernet Switches
Upstream sw itch Upstream sw itch Upstream sw itch Upstream sw itch
Designated port Designated port Designated port Designated port
changes to changes to changes to changes to
Forw arding state Forw arding state Forw arding state Forw arding state
Figure 1-3 The RSTP rapid transition mechanism
Upstream sw itch Upstream sw itch
Designated port Designated port
change to change to
Forw arding state Forw arding state
Figure 1-4 The MSTP rapid transition mechanism
Limitation on the combination of RSTP and MSTP exists to implement rapid transition.
For example, when the upstream switch adopts RSTP, the downstream switch adopts
MSTP and does not support RSTP 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 change to the Forwarding state after a period twice
the Forward Delay.
Some partners' switches adopt proprietary spanning tree protocols that are similar to
RSTP in the way to implement rapid transition on designated ports. When a switch of
this kind operates as the upstream switch of an S3100 series switch running MSTP, the
upstream designated port fails to change their states rapidly.
The rapid transition feature is developed to resolve this problem. When an S3100
series switch running MSTP is connected in the upstream direction to a partner's switch
running proprietary spanning tree protocol, you can enable the rapid transition feature
on the ports of the S3100 series switch operating as the downstream switch. 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,
Sends proposal packets to Sends proposal packets to Sends proposal packets to Sends proposal packets to
request rapid transition request rapid transition request rapid transition request rapid transition
Sends agreement packets Sends agreement packets Sends agreement packets Sends agreement packets
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
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Chapter 1 MSTP Configuration
Dow nstream switch Dow nstream switch Dow nstream switch Dow nstream switch
Root port blocks other Root port blocks other Root port blocks other Root port blocks other
non- non- non- non- -edge ports -edge ports, -edge ports -edge ports,
changes to Forwarding changes to Forwarding changes to Forwarding changes to Forwarding
state, and sends state, and sends state, and sends state, and sends
agreement packets agreement packets agreement packets agreement packets
to the upstream switch to the upstream switch to the upstream switch to the upstream switch
Root port Root port Root port Root port
Designated port Designated port Designated port Designated port
Dow nstream switch Dow nstream switch
Root port blocks Root port blocks
other non-edge ports other non-edge 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 sw itch to upstream sw itch
Root port Root port
Designated port Designated port