• 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 regardless of whether an agreement
packet from the upstream device is received.
Figure 18 shows the rapid state transition mechanism on MSTP designated ports.
Figure 18 Rapid state transition of an MSTP designated port
Figure 19 shows rapid state transition of an RSTP designated port.
Figure 19 Rapid state transition of an RSTP designated port
If the upstream device is a third-party device, the rapid state transition implementation might be limited.
For example, when the upstream device uses a rapid transition mechanism similar to that of RSTP, and the
downstream device adopts MSTP and does not work in RSTP mode, the root port on the downstream
device receives no agreement packet from the upstream device and sends no agreement packets to the
upstream device. As a result, the designated port of the upstream device fails to transit rapidly, and can
only change to the forwarding state after a period twice the Forward Delay.
You can enable the No Agreement Check feature on the port of the downstream device to enable the
designated port of the upstream device to transit its state rapidly.
Configuration prerequisites
Before you configure the No Agreement Check function, complete the following tasks:
• Connect a device is to a third-party upstream device that supports MSTP via a point-to-point link.
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