STPD Modes

An STPD has three modes of operation:

• 802.1D mode

  Use this mode for backward compatibility with previous STP versions and for compatibility with third-party switches using IEEE standard 802.1D. When configured in this mode, all rapid configuration mechanisms are disabled.

• 802.1w mode

  Use this mode for compatibility with Rapid Spanning Tree (RSTP). When configured in this mode, all rapid configuration mechanisms are enabled. The benefit of this mode is available on point-to-point links only and when the peer is likewise configured in 802.1w mode. If you do not select point-to-point links and the peer is not configured for 802.1w mode, the STPD fails back to 802.1D mode.

  You can enable or disable RSTP on a per STPD basis only; you cannot enable RSTP on a per port basis.

  For more information about RSTP and RSTP features, see Rapid Spanning Tree Protocol.

• MSTP mode

  Use this mode for compatibility with MSTP. MSTP is an extension of RSTP and offers the benefit of better scaling with fast convergence. When configured in this mode, all rapid configuration mechanisms are enabled. The benefit of MSTP is available only on point-to-point links and when you configure the peer in MSTP or 802.1w mode. If you do not select point-to-point links and the peer is not configured in 802.1w mode, the STPD fails back to 802.1D mode.

  You must first configure a CIST before configuring any MSTIs in the region. You cannot delete or disable a CIST if any of the MSTIs are active in the system.

  You can create only one MSTP region on the switch, and all switches that participate in the region must have the same regional configurations. You can enable or disable an MSTP on a per STPD basis only; you cannot enable MSTP on a per port basis.

  If configured in MSTP mode, an STPD uses the 802.1D BPDU encapsulation mode by default. To ensure correct operation of your MSTP STPDs, do not configure EMISTP or PVST+ encapsulation mode for MSTP STPDs.

  For more information about MSTP and MSTP features, see Multiple Spanning Tree Protocol.

By default:

• The STPD operates in 802.1D mode.

• The default device configuration contains a single STPD called s0.

• The default VLAN is a member of STPD s0 with autobind enabled.

To configure the mode of operation of an STPD, use the following command:

configure stpd stpd_name mode [dot1d | dot1w | mstp [cist | msti instance]]

All STP parameters default to the IEEE 802.1D values, as appropriate.