Configuration Prerequisites - H3C S7500X Series Configuration Manual

Figure 17 Rapid state transition of an MSTP designated port
Upstream device
The designated port
changes to the
forwarding state.
Figure 18 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.

Configuration prerequisites

Before you configure the No Agreement Check feature, complete the following tasks:
•
Connect a device to a third-party upstream device that supports spanning tree protocols
through a point-to-point link.
•
Configure the same region name, revision level, and VLAN-to-instance mappings on the two
devices.
(1) Proposal for rapid transition
(2) Agreement
(3) Agreement
Root port
(1) Proposal for rapid transition
(2) Agreement
Root port Designated port
43
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.