Specifications

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Catalyst 2950 and Catalyst 2955 Switch Command Reference

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Chapter 2 Cisco IOS Commands

clear spanning-tree detected-protocols

Use the clear spanning-tree detected-protocols privileged EXEC command to restart the protocol

migration process (force the renegotiation with neighboring switches) on all interfaces or on the

specified interface.

clear spanning-tree detected-protocols [interface interface-id]

This command is available only if your switch is running the enhanced software image (EI).

Syntax Description

Command Modes Privileged EXEC

Command History

Usage Guidelines A switch running both the Multiple Spanning Tree Protocol (MSTP) and the Rapid Spanning Tree

Protocol (RSTP) supports a built-in protocol migration mechanism that enables it to interoperate with

legacy 802.1D switches. If an MSTP and RSTP switch receives a legacy 802.1D configuration bridge

protocol data unit (BPDU) with the protocol version set to 0, it sends only 802.1D BPDUs on that port.

A multiple spanning-tree (MST) switch can also detect that a port is at the boundary of a region when it

receives a legacy BPDU, an MST BPDU (version 3) associated with a different region, or an RST BPDU

(version 2).

However, the switch does not automatically revert to the MSTP mode if it no longer receives 802.1D

BPDUs because it cannot determine whether the legacy switch has been removed from the link unless

the legacy switch is the designated switch. Use the clear spanning-tree detected-protocols command

in this situation.

Examples This example shows how to restart the protocol migration process on Fast Ethernet interface 0/1:

Switch# clear spanning-tree detected-protocols interface fastethernet0/1

interface interface-id (Optional) Restart the protocol migration process on the specified interface.

Valid interfaces include physical ports, VLANs, and port channels. The

valid VLAN range is 1 to 4094; do not enter leading zeros. The valid

port-channel range is 1 to 646.

Release Modification

12.1(9)EA1 This command was first introduced.