KB.15.15

same region. Use this setting to differentiate between region configurations in

situations such as the following:

• Changing configuration settings within a region where you want to track the

configuration versions you use

• Creating a new region from a subset of switches in a current region and want

to maintain the same region name.

• Using the pending option to maintain two different configuration options for

the same physical region.

This setting must be the same for all MSTP switches in the same MST region.

Range: 0 - 65535

Default: 0

NOTE: This option is available only when the switch is configured for MSTP

operation.

Setting the spanning tree compatibility mode

Syntax:

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.

stp-compatible The switch applies 802.1D STP operation on all ports.

rstp-operation 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.

mstp-operation The switch applies 802.1s MSTP operation on all ports

where compatibility with 802.1D or 802.1w spanning tree

protocols is not required.

NOTE: 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” (page 77), 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.

NOTE: When using MSTP rapid state transitions

Under some circumstances the rapid state transitions employed by MSTP can increase

the rates of frame duplication and misordering in the switched LAN. To allow MSTP

switches to support applications and protocols that may be sensitive to frame

duplication and misordering, 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.

Setting the time interval between listening, learning and forwarding states

Syntax:

spanning-tree forward-delay

80 Multiple instance spanning tree operation