Specifications

Spanning Tree Domains
ExtremeWare XOS 11.0 Concepts Guide 199
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.
To configure the mode of operation of an STPD, use the following command:
configure stpd <stpd_name> mode [dot1d | dot1w]
All STP parameters default to the IEEE 802.1D values, as appropriate.
Encapsulation Modes
You can configure ports within an STPD to accept specific BPDU encapsulations. This STP port
encapsulation is separate from the STP mode of operation. For example, you can configure a port to
accept the PVST+ BPDU encapsulation while running in 802.1D mode.
An STP port has three possible encapsulation modes:
• 802.1D mode
Use this mode for backwards 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
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
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.
To configure the BPDU encapsulation mode for one or more STP ports, use the following command:
configure stpd <stpd_name> ports mode [dot1d | emistp | pvst-plus] <port_list>
To configure the default BPDU encapsulation mode on a per STPD basis, use the following command:
configure stpd <stpd_name> default-encapsulation [dot1d | emistp | pvst-plus]
Instead of accepting the default encapsulation modes of dot1d for the default STPD s0 and emistp for
all other STPDs, this command allows you to specify the type of BPDU encapsulation to use for all
ports added to the STPD (if not otherwise specified).