HP MSR2000/3000/4000 Router Series Layer 2 - LAN Switching Configuration Guide

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[RouterB-Ethernet2/1] quit
[RouterB] stp global config-digest-snooping
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 regardless of whether an agreement
packet from the upstream device is received.
Figure 9 Rapid state transition of an MSTP designated port
Figure 10 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
Root port Designated port
Upstream device Downstream device
(1) Proposal for rapid transition
(3) Agreement
The root port blocks non-edge
ports.
The root port changes to the
forwarding state and sends an
Agreement to the upstream
device.
(2) Agreement
The designated port
changes to the
forwarding state.
Root port Designated port
Upstream device Downstream device
(1) Proposal for rapid transition
(2) Agreement
The root port blocks non-edge
ports, changes to the forwarding
state, and sends an Agreement to
the upstream device.
The designated
port changes to the
forwarding state.