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Configuring Spanning Tree Bridge Parameters Configuring Spanning Tree Parameters
page 5-18 OmniSwitch 6600 Family Network Configuration Guide April 2006
-> bridge forward delay 10
-> bridge cist forward delay 10
As in previous releases, it is possible to configure the flat mode instance with the bridge forward delay
command by specifying 1 as the instance number (e.g., bridge 1 forward delay 30). However, this is only
available when the switch is already running in the flat mode and STP or RSTP is the active protocol.
Note that the forward delay time is not configurable for 802.1s Multiple Spanning Tree Instances (MSTI).
These instances inherit the forward delay time from the flat mode instance (CIST).
Enabling/Disabling the VLAN BPDU Switching Status
By default, BPDU are not switched on ports associated with VLANs that have Spanning Tree disabled.
This may result in a network loop if the VLAN has redundant paths to one or more other switches. Allow-
ing VLANs that have Spanning Tree disabled to forward BPDU to all ports in the VLAN, can help to
avoid this problem.
To enable or disable BPDU switching on a VLAN, enter bridge followed by an existing VLAN ID (or
VLAN 1 if using a flat Spanning Tree instance) then bpdu-switching followed by enable or disable. For
example, the following commands enable BPDU switching on VLAN 10 and disable it on VLAN 20:
-> bridge 10 bpdu-switching enable
-> bridge 20 bpdu-switching disable
Note. Make sure that disabling BPDU switching on a Spanning Tree disabled VLAN will not cause
network loops to go undetected.
Configuring the Path Cost Mode
The path cost mode controls whether the switch uses a 16-bit port path cost (PPC) or a 32-bit PPC. When a
32-bit PPC switch connects to a 16-bit PPC switch, the 32-bit switch will have a higher PPC value that
will advertise an inferior path cost to the 16-bit switch. In this case, it may be desirable to set the 32-bit
switch to use STP or RSTP with a 16-bit PPC value.
By default, the path cost mode is set to automatically use a 16-bit value for all ports that are associated
with an STP (802.1D) instance or an RSTP (802.1w) instance and a 32-bit value for all ports associated
with an MSTP (802.1s) value. It is also possible to set the path cost mode to always use a 32-bit regard-
less of which protocol is active.
To change the path cost mode, use the bridge path cost mode command and specify either auto (uses
PPC value based on protocol) or 32bit.(always use a 32-bit PPC value). For example, the following
command changes the default path cost mode, which is automatic, to 32-bit mode:
-> bridge path cost mode 32bit