Configuring No Agreement Check
In RSTP and MSTP, the following types of messages are used for rapid state transition on designated ports:
Proposal—Sent by designated ports to request rapid transition
Agreement—Used to acknowledge rapid transition requests
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 41: Rapid state transition of an MSTP designated port
Figure 42: 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 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.
It sends no agreement to the upstream device.
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.