Brocade Multi-Service IronWare Switching Configuration Gui Manual de usuario descargar pdf (Pagina 457)

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Multi-Service IronWare Switching Configuration Guide 427

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Convergence in a simple topology

Convergence at link restoration

When Port2/Switch 2 is restored, both Switch 2 and Switch 1 recognize the change. Port2/Switch

1 starts assuming the role of a Designated port and sends an RST BPDU containing a proposal flag

to Port2/Switch 2.

When Port2/Switch 2 receives the RST BPDUs, RSTP algorithm determines that the RST BPDUs the

port received are better than those received on Port3/Switch 3; therefore, Port2/Switch 2 is given

the role of a Root port. All the ports on Switch 2 are informed that a new Root port has been

assigned which then signals all the ports to synchronize their roles and states. Port3/Switch 2,

which was the previous Root port, enters a discarding state and negotiates with other ports on the

bridge to establish its new role and state, until it finally assumes the role of a Designated port.

Next, the following happens:

• Port3/Switch 2, the Designated port, sends an RST BPDU, with a proposal flag to Port3/Switch

• Port2/Switch 2 also sends an RST BPDU with an agreed flag to Port2/Switch 1 and then

places itself into a forwarding state.

When Port2/Switch 1 receives the RST BPDU with an agreed flag sent by Port2/Switch 2, it puts

that port into a forwarding state. The topology is now fully converged.

When Port3/Switch 3 receives the RST BPDU that Port3/Switch 2 sent, RSTP algorithm determines

that these RST BPDUs are superior to those that Port3/Switch 3 can transmit. Therefore,

Port3/Switch 3 is given a new role, that of an Alternate port. Port3/Switch 3 immediately enters a

discarding state.

Now Port3/Switch 2 does not go into a forwarding state instantly like the Root port. It waits until the

forward delay timer expires twice on that port while it is still in a Designated role, before it can

proceed to the forwarding state. The wait, however, does not cause a denial of service, since the

essential connectivity in the topology has already been established.

When fully restored, the topology is the same as that shown on Figure 86.

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