H3C S7500E-X Configuration Manual page 104

Both RSTP and MSTP devices can perform rapid transition on a designated port only when the port
receives an agreement packet from the downstream device. RSTP and MSTP devices have the
following differences:
•
For MSTP, the root port of the downstream device sends an agreement packet only after it
receives an agreement packet from the upstream device.
•
For RSTP, the downstream device sends an agreement packet whether or not an agreement
packet from the upstream device is received.
Figure 25 Rapid state transition of an MSTP designated port
Upstream device
The designated port
changes to the
forwarding state.
Figure 26 Rapid state transition of an RSTP designated port
Upstream device
The designated
port changes to the
forwarding state.
If the upstream device is a third-party device, the rapid state transition implementation might be
limited as follows:
•
The upstream device uses a rapid transition mechanism similar to that of RSTP.
•
The downstream device runs MSTP and does not operate in RSTP mode.
In this case, the following occurs:
The root port on the downstream device receives no agreement from the upstream device.
1.
It sends no agreement to the upstream device.
2.
As a result, the designated port of the upstream device can transit to the forwarding state only after a
period twice the Forward Delay.
To enable the designated port of the upstream device to transit its state rapidly, enable No
Agreement Check on the downstream device's port.
(1) Proposal for rapid transition
(2) Agreement
(3) Agreement
Root port
(1) Proposal for rapid transition
(2) Agreement
Root port Designated port
91
Downstream device
The root port blocks non-edge
ports.
The root port changes to the
forwarding state and sends an
Agreement to the upstream
device.
Designated port
Downstream device
The root port blocks non-edge
ports, changes to the forwarding
state, and sends an Agreement to
the upstream device.