Spanning Tree Domains; Member Vlans - Extreme Networks ExtremeWare XOS Guide Manual

Spanning Tree Domains

Spanning Tree Domains
The switch can be partitioned into multiple virtual bridges. Each virtual bridge can run an independent
Spanning Tree instance. Each Spanning Tree instance is called a Spanning Tree Domain (STPD). Each
STPD has its own root bridge and active path. After an STPD is created, one or more VLANs can be
assigned to it.
A physical 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.
To create an STPD, use the following command:
create stpd <stpd_name>
To delete an STPD, use the following command:
delete stpd <stpd_name>
For more detailed information about configuring STP and STP parameters, see "Configuring STP on the
Switch" on page 159.

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 EMISTP or PVST+ encapsulated BPDUs (see
"Encapsulation Modes" on page 139 for more information about encapsulating STP BPDUs). Only one
carrier VLAN can exist in a given STP domain although some of its ports can be outside the control of
any STP domain at the same time.
The carrier VLAN's StpdID must be identical to the VLANid of one of the member VLANs in that STP
domain. See the section "Specifying the Carrier VLAN" on page 138, for an example.
Protected VLAN
Protected VLANs are all other VLANs that are members of the STP domain but do not define the scope
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 STP domains, but any particular port in the VLAN
can belong to only one STP domain. Also known as non-carrier VLANs.
ExtremeWare XOS 10.1 Concepts Guide 137