User guide

192 ExtremeWare 7.2e Installation and User Guide
Spanning Tree Protocol (STP)
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.
NOTE
A VLAN can span multiple STPDs. However, on the Summit 400, there is a hardware limitation that
restricts each physical port to a single STPD. If the Summit 400 port is already a member of an STPD,
then that port cannot be in another VLAN that is in a different STPD, or not in a STPD at all.
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.
• When STP blocks a path, no data can be transmitted or received on the blocked port.
• Within any given STPD, all VLANs belonging to it use the same spanning tree.
If you delete a STPD, the VLANs that were members of that STPD are also deleted. You must remove
all VLANs associated with the STP before deleting the STPD to preserve the VLAN configuration.
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. This mode is available for point-to-point links only.
RSTP is enabled or disabled on a per STPD basis only. You do not enable RSTP on a per port basis.
For more information about RSTP and RSTP features, see “Rapid Spanning Tree Protocol” on
page 198.
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
To configure the mode of operation of an STPD, use the following command:
configure stpd <spanning tree name> mode [dot1d | dot1w]
All STP parameters default to the IEEE 802.1d values, as appropriate.