Cisco 7609-S Software Configuration Guide - Page 258

Understanding RSTP Chapter 19 Configuring Standard-Compliant IEEE MST Figure 19-4 Proposal and Agreement Handshaking for Rapid Convergence Switch A Proposal Switch B Root F Agreement Designated switch F DP RP Root F DP Designated switch F RP Proposal Switch C Root F DP Designated switch F F RP DP Agreement F RP DP = designated port RP = root port F = forwarding 88760 Synchronization of Port Roles When the router 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 router is synchronized with superior root information received on the root port if all other ports are synchronized. An individual port on the router is synchronized if: • That port is in the blocking state. • It is an edge port (a port configured to be at the edge of the network). If a designated port is in the forwarding state and is not configured as an edge port, 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 that all of the ports are synchronized, the router sends an agreement message to the designated router corresponding to its root port. When the routers 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 19-5. 19-12 Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX OL-4266-08