Synchronization Of Port Roles - Cisco Catalyst 3750-E Software Configuration Manual

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Configuring MSTP

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.

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.

In a switch stack, the cross-stack rapid transition (CSRT) feature ensures that a stack member

receives acknowledgments from all stack members during the proposal-agreement handshaking

before moving the port to the forwarding state. CSRT is automatically enabled when the switch is

in MST mode.

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.

Proposal and Agreement Handshaking for Rapid Convergence

That port is in the blocking state.

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

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

Understanding RSTP

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