R2511-HP MSR Router Series Layer 2 - LAN Switching Configuration Guide(V5)

67
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 regardless of whether an agreement
packet is received from the upstream device.
Figure 19 Rapid state transition of an MSTP designated port
Figure 20 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 operate 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 that is twice the Forward Delay.
You can enable the No Agreement Check feature on the downstream device's port 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: