Chapter 17 Stp Commands - Extreme Networks ExtremeWare Command Reference Manual

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STP Commands

• When STP blocks a path, no data can be transmitted or received on the blocked port.

• Within any given STPD, all VLANs belonging to it use the same spanning tree.

If you delete a STPD, the VLANs that were members of that STPD are also deleted. You must remove

all VLANs associated with the STP before deleting the STPD.

An STPD has two 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. This mode is available for point-to-point links only.

RSTP is enabled or disabled on a per STPD basis only. You do not enable RSTP on a per port basis.

By default, the following conditions exist:

• 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.

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

An STP port has three modes of operation:

• 802.1d mode

This mode is used for backward compatibility with previous STP versions and for compatibility with

third-party switches using IEEE standard 802.1d. BPDUs are sent untagged in 802.1d mode. Because

of this, on any given physical interface there can be only one STPD running in 802.1d mode.

• Extreme Multiple Instance Spanning Tree Protocol (EMISTP) mode

EMISTP mode is an extension of STP that allows a physical port to belong to multiple STPDs by

assigning the port to multiple VLANs. EMISTP adds significant flexibility to STP network design.

BPDUs are sent with an 802.1Q tag having an STPD instance Identifier (StpdID) in the VLANid field.

• PVST+ mode

This mode implements PVST+ in compatibility with third-party switches running this version of STP.

The STPDs running in this mode have a one-to-one relationship with VLANs, and send and process

packets in PVST+ format.

These port modes are for STP ports, not for physical ports. When a physical port belongs to multiple

STPDs, it is associated with multiple STP ports It is possible for the physical port to run in different

modes for different domains to which it belongs.

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