Configuring Spanning Tree Parameters Configuring STP Bridge Parameters
OmniSwitch 6800/6850/9000 Network Configuration Guide March 2008 page 7-17
Primary port functionality. The path cost assigned to the aggregate link is not the same between
OmniSwitch and Cisco switches since vendor-specific formulas are used to derive the path cost.
Manual configuration is recommended to match the Cisco path cost assignment for an aggregate link.
For more information on the configuration of path cost for aggregate links, refer “Path Cost for Link
Aggregate Ports” on page 7-33.
The table below shows the default Spanning Tree values.
Configuring STP Bridge Parameters
The Spanning Tree software is active on all switches by default and uses default bridge and port parame-
ter values to calculate a loop free topology. It is only necessary to configure these parameter values if it is
necessary to change how the topology is calculated and maintained.
Note the following when configuring Spanning Tree bridge parameters:
• When a switch is running in the 1x1 Spanning Tree mode, each VLAN is in essence a virtual bridge
with its own Spanning Tree instance and configurable bridge parameters.
• When the switch is running in the flat mode and STP (802.1D) or RSTP (802.1w) is the active proto-
col, bridge parameter values are only configured for the flat mode instance.
• If MSTP (802.1s) is the active protocol, then the priority value is configurable for each Multiple Span-
ning Tree Instance (MSTI). All other parameters, however, are still only configured for the flat mode
instance and are applied across all MSTIs.
• Bridge parameter values for a VLAN instance are not active unless Spanning Tree is enabled on the
VLAN and at least one active port is assigned to the VLAN. Use the vlan stp command to enable or
disable a VLAN Spanning Tree instance.
• If Spanning Tree is disabled on a VLAN, active ports associated with that VLAN are excluded from
Spanning Tree calculations and will remain in a forwarding state.
• Note that when a switch is running in the flat mode, disabling Spanning Tree on VLAN 1 disables the
instance for all VLANs and all active ports are then excluded from any Spanning Tree calculations and
will remain in a forwarding state.
Parameters OmniSwitch Cisco
Mac Reduction Mode Enabled Disabled
Bridge Priority 32768 32768
Port Priority 128 32 (catOS) / 128 (IOS)
Port Path Cost IEEE Port Speed Table IEEE Port Speed Table
Aggregate Path Cost Proprietary Table Avg Path Cost / NumPorts
Default Path Cost Mode Short (16-bit) Short (16-bit)
Max Age 20 20
Hello Time 2 2
Forward Delay Time 15 15
Default Protocol RSTP (1w) Per Vlan PVST+ (1d) Per Switch
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