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Chapter 2
Catalyst 3560 Switch 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.
Syntax Description
interface interface-id
Defaults
No default is defined.
Command Modes
Privileged EXEC
Command History
Release
12.1(19)EA1
Usage Guidelines
A switch running the rapid per-VLAN spanning-tree plus (rapid-PVST+) protocol or the Multiple
Spanning Tree Protocol (MSTP) supports a built-in protocol migration mechanism that enables it to
interoperate with legacy IEEE 802.1D switches. If a rapid-PVST+ switch or an MSTP switch receives a
legacy IEEE 802.1D configuration bridge protocol data unit (BPDU) with the protocol version set to 0,
it sends only IEEE 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 a rapid spanning-tree (RST) BPDU (Version 2).
However, the switch does not automatically revert to the rapid-PVST+ or the MSTP mode if it no longer
receives IEEE 802.1D BPDUs because it cannot learn 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 a port:
Switch# clear spanning-tree detected-protocols interface gigabitethernet0/1
Related Commands
Command
show spanning-tree
spanning-tree link-type
78-16405-05
clear spanning-tree detected-protocols [interface interface-id]
(Optional) Restart the protocol migration process on the specified interface.
Valid interfaces include physical ports, VLANs, and port channels. The
VLAN range is 1 to 4094. The port-channel range is 1 to 48.
Modification
This command was introduced.
Description
Displays spanning-tree state information.
Overrides the default link-type setting and enables rapid spanning-tree
changes to the forwarding state.
Catalyst 3560 Switch Command Reference
clear spanning-tree detected-protocols
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