Stp Rules And Restrictions - Extreme Networks ExtremeWare XOS Command Reference Manual

An STP port has three possible encapsulation modes:
802.1D mode
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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, any given physical interface can have only one STPD running in 802.1D mode.
Extreme Multiple Instance Spanning Tree Protocol (EMISTP) mode
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EMISTP mode is proprietary to Extreme Networks and 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.
Per VLAN Spanning Tree (PVST+) mode
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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 encapsulation 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.

STP Rules and Restrictions

This section summarizes the rules and restrictions for configuring STP as follows:
The carrier VLAN must span all ports of the STPD.
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The StpdID must be the VLANid of the carrier VLAN; the carrier VLAN cannot be partitioned.
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A default VLAN cannot be partitioned. If a VLAN traverses multiple STPDs, the VLAN must be
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tagged.
An STPD can carry, at most, one VLAN running in PVST+ mode, and its StpdID must be identical
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with that VLANid. In addition, the PVST+ VLAN cannot be partitioned.
The default VLAN of a PVST+ port must be identical with the native VLAN on the PVST+ device
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connected to that port.
If an STPD contains both PVST+ and non-PVST+ ports, that STPD must be enabled. If that STPD is
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disabled, the BPDUs are flooded in the format of the incoming STP port, which may be incompatible
with those of the connected devices.
The 802.1D ports must be untagged; and the EMISTP/PVST+ ports must be tagged in the carrier
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VLAN.
An STPD with multiple VLANs must contain only VLANs that belong to the same virtual router
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instance.
Automatically adding ports to an STPD (known as STP autobind) cannot be configured on a
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Netlogin VLAN.
STP cannot be configured on the following ports:
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A mirroring target port.
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A software-controlled redundant port.
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A Netlogin port.
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ExtremeWare XOS 11.3 Command Reference
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