Specifications

196 ExtremeWare XOS 11.0 Concepts Guide
Spanning Tree Protocol
Table 36 describes the terms associated with the Extreme Networks implementation of STP.
Table 36: STP terms
Term Description
Autobind If enabled, autobind automatically adds or removes ports from the Spanning Tree
Domain (STPD). If ports are added to the carrier VLAN, the member ports of the
VLAN are automatically added to the STPD. If ports are removed from the carrier
VLAN, those ports are also removed from the STPD. For more information about the
autobind feature and adding ports to an STPD, see “Binding Ports” on page 200.
Carrier VLAN Carrier VLANs define the scope of the STPD including the physical and logical ports
that belong to the STPD and the 802.1Q tag used to transport EMISTP or PVST+
encapsulated Bridge Protocol Data Units (BPDUs). Only one carrier VLAN can exist
in any given STPd. For more information about carrier VLANs, see “Member VLANs”
on page 197.
Default encapsulation
mode
Default encapsulation allows you to specify the type of BPDU encapsulation to use
for all ports added to a given STPD if not otherwise specified, not just one individual
port. By default, all ports in user-created STPDs are in emistp mode. All ports in
the default STPD s0 are in 802.1d mode.
The three possible encapsulation modes are:
• 802.1D—This mode is used for backward compatibility with previous STP
versions and for compatibility with third-party switches using IEEE standard
802.1D.
• EMISTP—The Extreme Multiple Instance Spanning Tree Protocol (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.
• PVST+ —This mode implements Per VLAN Spanning Tree (PVST+) in
compatibility with third-party switches running this version of STP.
For more information about how to configure the default encapsulation mode, see
“Encapsulation Modes” on page 199.
Encapsulation mode You can configure ports within an STPD to accept and transmit specific BPDU
encapsulations. By default, all ports in user-created STPDs are in emistp mode. All
ports in the default STPD s0 are in 802.1d mode. The three possible encapsulation
modes are:
• 802.1d—This mode is used for backward compatibility with previous STP versions
and for compatibility with third-party switches using IEEE standard 802.1d.
• EMISTP—The EMISTP mode is an extension of STP that allows a physical port
to belong to multiple STPDs by assigning the port to multiple VLANs.
• PVST+ —This mode implements PVST+ in compatibility with third-party switches
running this version of STP.
For more information about how to configure encapsulation modes, see
“Encapsulation Modes” on page 199.
Protected VLAN Protected VLANs are VLANs other than the carrier VLAN that are members of the
STPD. 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. Also known
as non-carrier VLANs. For more information about protected VLANs, see “Member
VLANs” on page 197.
Spanning Tree Domain An STP instance that contains one or more VLANs. The switch can run multiple
STPDs. For more information about STPDs, see “Spanning Tree Domains” on
page 197.