Extreme Networks ExtremeWare XOS Command Reference Manual page 494

STP Commands
A port can belong to multiple STPDs. In addition, a VLAN can span multiple STPDs.
The key points to remember when configuring VLANs and STP are:
• Each VLAN forms an independent broadcast domain.
• STP blocks paths to create a loop-free environment.
• Within any given STPD, all VLANs belonging to it use the same spanning tree.
Member VLANs
When you add a VLAN to an STPD, that VLAN becomes a member of the STPD. The two types of
member VLANs in an STPD are:
• Carrier
• Protected
Carrier VLAN. A carrier VLAN defines the scope of the STPD, which includes the physical and logical
ports that belong to the STPD and the 802.1Q tag used to transport Extreme Multiple Instance Spanning
Tree Protocol (EMISTP) or Per VLAN Spanning Tree (PVST+) encapsulated Bridge Protocol Data Units
(BPDUs). Only one carrier VLAN can exist in a given STPD, although some of its ports can be outside
the control of any STPD at the same time.
NOTE
The StpdID must be identical to the VLANid of the carrier VLAN in that STPD.
Protected VLAN. Protected VLANs are all other VLANs that are members of the STPD. These VLANs
"piggyback" on the carrier VLAN. Protected VLANs do not transmit or receive STP BPDUs, but they
are affected by STP state changes and inherit the state of the carrier VLAN. Protected VLANs can
participate in multiple STPD, but any particular port in the VLAN can belong to only one STPD. Also
known as non-carrier VLANs.
STPD Modes
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. The benefit of this mode is available on
point-to-point and edge ports only.
You enable or disable RSTP on a per STPD basis only. You do not enable RSTP on a per port basis.
By default, the:
• STPD operates in 802.1D mode.
• Default device configuration contains a single STPD called s0.
• Default VLAN is a member of STPD s0 with autobind enabled.
494 ExtremeWare XOS 11.0 Command Reference Guide