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Ethernet Card Software Feature and Configuration Guide, R7.2
January 2009
Chapter 7 Configuring STP and RSTP
Synchronization of Port Roles
Figure 7-4 Proposal and Agreement Handshaking for Rapid Convergence
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 synchron ized.

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 po rt 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.

Proposal
FF
RPDP
FF
RPDP
FF
RPDP
FF
RPDP
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Agreement
Root
Switch A
Switch A
Switch A
Switch A
Switch B
Switch B
Switch B
Switch B
Switch B
Switch B
Proposal
Agreement
DP = designated port
RP = root port
F = forwarding
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Root
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Root
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