4-33Figure 4-7 shows the rapid state transition mechanism on MSTP designated ports.Figure 4-7 Rapid state transition of an MSTP designated portFigure 4-8 shows rapid state transition of an RSTP designated port.Figure 4-8 Rapid state transition of an RSTP designated portRoot portDesignated portRoot port blocks other non-edge ports, changes toforwarding state and sendsAgreement to upstream deviceUpstream device Downstream deviceProposal for rapid transitionAgreementDesignated portchanges toforwarding stateIf the upstream device is a third-party device, the rapid state transition implementation may 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 thedownstream device receives no agreement packet from the upstream device and thus sends noagreement packets to the upstream device. As a result, the designated port of the upstream devicefails to transit rapidly and can only change to the forwarding state after a period twice the ForwardDelay.In this case, you can enable the No Agreement Check feature on the downstream device’s port toenable the designated port of the upstream device to transit its state rapidly.Configuration Prerequisitesz A device is connected to a third-party upstream device supporting MSTP via a point-to-point link.z Configure the same region name, revision level and VLAN-to-instance mappings on the twodevices, thus assigning them to the same region.Configuring the No Agreement Check functionTo make the No Agreement Check feature take effect, enable it on the root port.Follow these steps to configure No Agreement Check:
