Synchronization Of Port Roles - Cisco Catalyst 3750 Software Configuration Manual

Metro switch

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Table of Contents

Understanding RSTP

Figure 15-2 Proposal and Agreement Handshaking for Rapid Convergence

DP = designated port

RP = root port

F = forwarding

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. An individual port on the switch is synchronized if

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 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

Catalyst 3750 Metro Switch Software Configuration Guide

When Switch C is connected to Switch B, a similar set of handshaking messages are exchanged.

Switch C selects the port connected to Switch B as its root port, and both ends immediately

transition to the forwarding state. With each iteration of this handshaking process, one more switch

joins the active topology. As the network converges, this proposal-agreement handshaking

progresses from the root toward the leaves of the spanning tree.

The switch learns the link type from the port duplex mode: a full-duplex port is considered to have

a point-to-point connection; a half-duplex port is considered to have a shared connection. You can

override the default setting that is controlled by the duplex setting by using the spanning-tree

link-type interface configuration command.

That port is in the blocking state.

It is an edge port (a port configured to be at the edge of the network).

Configuring MSTP