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Using 802.1s Multiple Spanning Tree MST Configuration Overview
OmniSwitch 6600 Family Network Configuration Guide April 2006 page 6-11
Implicit commands resemble previously implemented Spanning Tree commands, but apply to the appro-
priate instance based on the current mode and protocol that is active on the switch. For example, if the 1x1
mode is active, the instance number specified with the following command implies a VLAN ID:
-> bridge 255 priority 16384
If the flat mode is active, the single flat mode instance is implied and thus configured by the command.
Since the flat mode instance is implied in this case, there is no need to specify an instance number. For
example, the following command configures the protocol for the flat mode instance:
-> bridge protocol mstp
Similar to previous releases, it is possible to configure the flat mode instance by specifying 1 for the
instance number (e.g., bridge 1 protocol rstp). However, this is only available when the switch is already
running in the flat mode and STP or RSTP is the active protocol.
Note. When a snapshot is taken of the switch configuration, the explicit form of all Spanning Tree
commands is captured. For example, if the priority of MSTI 2 was changed from the default value to a
priority of 16384, then bridge msti 2 priority 16384 is the command captured to reflect this in the snap-
shot file. In addition, explicit commands are captured for both flat and 1x1 mode configurations.
For more information about Spanning Tree configuration commands as they apply to all supported proto-
cols (STP, RSTP, and MSTP), see Chapter 5, “Configuring Spanning Tree Parameters.”
Understanding Spanning Tree Modes
The switch can operate in one of two Spanning Tree modes: flat and 1x1. The flat mode provides a
Common Spanning Tree (CST) instance that applies across all VLANs by default. This mode supports the
use of the STP (802.1D), RSTP (802.1w), and MSTP (802.1s) protocols. MSTP allows the mapping of
one or more VLANs to a single Spanning Tree instance.
The 1x1 mode is an Alcatel proprietary implementation that automatically calculates a separate Spanning
Tree instance for each VLAN configured on the switch. This mode only supports the use of the STP and
RSTP protocols.
Although MSTP is not supported in the 1x1 mode, it is possible to define an MSTP configuration in this
mode using explicit Spanning Tree commands. See “Using Spanning Tree Configuration Commands” on
page 6-10 for more information about explicit commands.
By default, a switch is running in the 1x1 mode and using the 802.1D protocol when it is first turned on.
See Chapter 5, “Configuring Spanning Tree Parameters,” for more information about Spanning Tree
modes.