H3C Technologies H3C S7500E Series Switches - Manual (Page 189)

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Figure 13-8 Rapid state transition of an RSTP designated port
Root port
Designated port
Root port blocks other non-
edge ports, changes to
forwarding state and sends
Agreement to upstream device
Upstream device Downstream device
Proposal for rapid transition
Agree
ment
Designated port
changes to
forwarding state
If 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 the
downstream device receives no agreement packet from the upstream device and thus 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.
In this case, 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
A device is connected to a third-party upstream device supporting MSTP via a point-to-point link.
Configure the same region name, revision level and VLAN-to-instance mappings on the two
devices, thus assigning them to the same region.
Configuring the No Agreement Check function
To make the No Agreement Check feature take effect, enable it on the root port.
Follow these steps to configure No Agreement Check:
To do... Use the command... Remarks
Enter system view system-view —
Enter Ethernet interface
view, or Layer 2
aggregate interface
view
interface interface-type
interface-number
Enter interface
or port group
view
Enter port group view
port-group manual
port-group-name
Required
Use either command.
Enable No Agreement Check stp no-agreement-check
Required
Disabled by default