Cisco Systems Cisco ONS 15310-MA, ONS 15310-CL manual Synchronization of Port Roles

Chapter 7 Configuring STP and RSTP on the ML-Series Card

RSTP Features

Figure 7-4

ML-Series

Proposal and Agreement Handshaking for Rapid Convergence

Proposal ML-Series

Switch A Switch B

Root Agreement

F

DP

Switch A

ML-Series

F

RP Switch B

Root

F

DP

Switch A

Root

F

DP

Switch A

DP = designated port RP = root port

F = forwarding

ML-Series	Proposal	ML-Series
F
RP
Switch B		Switch B

	ML-Series		Agreement		ML-Series
F		F			F
RP		DP		RP
	Switch B				Switch B
				124086

Synchronization of Port Roles

When the switch receives a proposal message on one of its ports and that port is selected as the new root port, the RSTP forces all other ports to synchronize with the new root information. The switch is synchronized with superior root information received on the root port if all other ports are synchronized.

If a designated port is in the forwarding state, it transitions to the blocking state when the RSTP forces it to synchronize with new root information. In general, when the RSTP forces a port to synchronize with root information and the port does not satisfy any of the above conditions, its port state is set to blocking.

After ensuring all of the ports are synchronized, the switch sends an agreement message to the designated switch corresponding to its root port. When the switches connected by a point-to-point link are in agreement about their port roles, the RSTP immediately transitions the port states to forwarding. The sequence of events is shown in Figure 7-5.

Cisco ONS 15310-CL, ONS 15310-MA, and ONS 15310-MA SDH Ethernet Card Software Feature and Configuration Guide, R9.1 and R9.2

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