Alcatel-Lucent 060321-10, Rev. B, Справочное руководство CLI

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Distributed Spanning Tree Commands spantree mode
OmniSwitch CLI Reference Guide March 2011 page 5-3
spantree mode
Selects the flat Spanning Tree or per-VLAN Spanning Tree operating mode for the switch. These modes
are exclusive; however, it is not necessary to reboot the switch when the STP modes are changed.
spantree mode { flat | per-vlan}
Syntax Definitions
flat One Spanning Tree instance per switch.
per-vlan One Spanning Tree instance for each VLAN configured on a switch.
Defaults
By default, the Spanning Tree mode for the switch is set to per-VLAN.
Platforms Supported
OmniSwitch 10K
Usage Guidelines
•
The Multiple Spanning Tree Protocol (MSTP), as defined in the IEEE 802.1Q 2005 standard, is only
supported on switches operating in the flat Spanning Tree mode.
•
If standard STP or RSTP is used when the switch is running in the flat mode, a single STP instance is
applied across all VLANs. For example, if a port belonging to VLAN 10 and a port belonging to
VLAN 20 connect to the same switch together, then STP blocks one of these ports.
•
If MSTP is used when the switch is running in the flat mode, a single STP instance is applied to each
Multiple Spanning Tree Instance (MSTI). Each MSTI represents a set of VLANs.
•
Flat Spanning Tree mode supports fixed (untagged) and 802.1Q tagged ports in each VLAN. However,
Bridge Protocol Data Units (BPDUs) are always untagged.
•
If the per-VLAN mode is selected, a single Spanning Tree instance is enabled for each VLAN config-
ured on the switch. For example, if there are five VLANs configured on the switch, then there are five
separate Spanning Tree instances. In essence, a VLAN is a virtual bridge that has its own bridge ID
and
configurable STP parameters, such as protocol, priority, hello time, max-age, and forward delay.
•
When operating in per-VLAN mode, 802.1Q tagged ports participate in an 802.1Q Spanning Tree
instance that allows the Spanning Tree to extend across tagged VLANs. As a result, a tagged port can
participate in more than one Spanning Tree instance; one for each VLAN that the port carries.
•
If a VLAN contains both fixed and tagged ports and the switch is operating in per-VLAN Spanning
Tree mode, then a hybrid of the two Spanning Tree instances (single and 802.1Q) is applied. If a
VLAN appears as a tag on a port, then the BPDU for that VLAN are also tagged. However, if a VLAN
appears as the configured default VLAN for the port, then BPDU are not tagged and the single Span-
ning Tree instance applies.
•
Regardless of which mode the switch is running in, it is possible to administratively disable the
Spanning Tree status for an individual VLAN (see
Chapter 4, “VLAN Management Commands” ).