Setting the spanning tree compatibility mode


spanning-tree force-version [ stp-compatible | rstp-operation | mstp-operation ]

Sets the spanning tree compatibility mode. This command forces the switch to emulate behavior of earlier versions of spanning tree protocol, or return to MSTP behavior. The command is useful in test or debug applications, and removes the need to reconfigure the switch for temporary changes in spanning tree operation.


The switch applies 802.1D STP operation on all ports.


The switch applies 802.1w operation on all ports except those ports where it detects a system using 802.1D Spanning Tree. RSTP is Rapid Spanning Tree Protocol.


The switch applies 802.1s MSTP operation on all ports where compatibility with 802.1D or 802.1w spanning tree protocols is not required.


Even when mstp-operation is selected, if the switch detects an 802.1D BPDU or an 802.1w BPDU on a port, it communicates with the device linked to that port using STP or RSTP BPDU packets. Also, if errors are encountered as described in Configuring MSTP at a glance, setting force-version to stp-compatible forces the MSTP switch to communicate out all ports using operations that are compatible with IEEE 802.1D STP.


When using MSTP rapid state transitions

Under some circumstances the rapid state transitions employed by MSTP can increase the rates of frame duplication and incorrect ordering in the switched LAN. To allow MSTP switches to support applications and protocols that may be sensitive to frame duplication and incorrect ordering, setting the Force Protocol Version (force-version) parameter to stp-compatible allows MSTP to operate with rapid transitions disabled. The value of this parameter applies to all ports on the switch.