Prerequisites - H3C S5500-SI Series Operation Manual

Operation Manual – MSTP
H3C S5500-SI Series Ethernet Switches
Figure 1-7 and Figure 1-8 show the rapid state transition mechanism on MSTP and
RSTP designated ports.
Upstream switch Upstream switch
Designated port Designated port
changes to
Forwarding state Forwarding state
Figure 1-7 Rapid state transition mechanism on the MSTP designated port
Upstream switch Upstream switch Upstream switch Upstream switch
Designated port Designated port Designated port Designated port
changes to changes to changes to changes to
Forwarding state Forwarding state Forwarding state Forwarding state
Figure 1-8 Rapid state transition mechanism on the RSTP designated port
If the upstream device comes from another vendor, the rapid state transition
implementation may be limited. For example, when the upstream device adopts RSTP,
the downstream device adopts MSTP and does not support RSTP mode, the root port
on the downstream device receives no agreement packet from the upstream device
and thus sends no agreement packets to the upstream device. 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.
In this case, you can enable the No Agreement Check feature on the downstream
device's port to perform rapid state transition.

1.7.1 Prerequisites

A device is the upstream one that is connected to another vendor's MSTP
supported device via a point-to-point link.
Send proposal packet
to request rapid transition to request rapid transition
Send agreement packet
Send agreement packet
Send agreement packets
Sends proposal packet 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
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Chapter 1 MSTP Configuration
Downstream switch Downstream switch
Root port blocks Root port blocks
other non-edge ports other non-edge ports - -
Root port changes to Root port changes to
Forwarding state and Forwarding state and
sends agreement packet
to upstream switch to upstream switch
Root port Root port
Designated port Designated port
Downstream switch Downstream switch Downstream switch Downstream switch
Root port blocks other Root port blocks other Root port blocks other Root port blocks other
non- non- non- non- - -edge ports - -
changes to Forwarding changes to Forwarding changes to Forwarding changes to Forwarding
state, and sends state, and sends state, and sends
agreement packet
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