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Configuring Spanning Tree Parameters Configuring STP Bridge Parameters
OmniSwitch AOS Release 7 Network Configuration Guide June 2013 page 6-27
The following sections provide information and procedures for using the bridge configuration commands
and also includes command examples.
Selecting the Spantree Protocol
The switch supports three Spanning Tree protocols: STP, RSTP (the default), MSTP. To configure the
Spanning Tree protocol for a VLAN instance regardless of which mode (per-VLAN or flat) is active for
the switch, use the
spantree protocol command with the vlan parameter. For example, the following
command changes the protocol to RSTP for VLAN 455:
-> spantree vlan 455 protocol rstp
Note. When configuring the protocol value for a VLAN instance, MSTP is not an available option. This
protocol is only supported on the flat mode instance.
To configure the protocol for the flat mode CIST instance, use either the spantree protocol command or
the spantree protocol command with the cist parameter. Note that both commands are available when the
switch is running in either mode (per-VLAN or flat). For example, the following commands configure the
protocol for the flat mode instance to MSTP:
-> spantree cist protocol mstp
-> spantree protocol mstp
Configuring the Bridge Priority
A bridge is identified within the Spanning Tree by its bridge ID (an eight byte hex number). The first two
bytes of the bridge ID contain a priority value and the remaining six bytes contain a bridge MAC address.
The bridge priority is used to determine which bridge serves as the root of the Spanning Tree. The lower
the priority value, the higher the priority. If more than one bridge have the same priority, then the bridge
with the lowest MAC address becomes the root.
Note. Configuring a Spanning Tree bridge instance with a priority value that causes the instance to
become the root is recommended, instead of relying on the comparison of switch base MAC addresses to
determine the root.
If the switch is running in the per-VLAN Spanning Tree mode, then a priority value is assigned to each
VLAN instance. If the switch is running in the flat Spanning Tree mode, the priority is assigned to the flat
mode instance or a Multiple Spanning Tree Instance (MSTI). In both cases, the default priority value is
assigned. Note that priority value for an MSTI must be a multiple of 4096.
spantree path-cost-mode Configuring the automatic selection of a 16-bit path cost for STP/
RSTP ports and a 32-bit path cost for MSTP ports or sets all path
costs to use a 32-bit value.
spantree auto-vlan-contain-
ment Enables or disables Auto VLAN Containment (AVC) for 802.1s
instances.
spantree pvst+compatibility Enables or disables PVST+ mode on the switch.
Commands Used for ...