Configuring Spanning Tree Parameters Configuring STP Port Parameters
OmniSwitch 6800/6850/9000 Network Configuration Guide March 2008 page 7-33
To change the port path cost value for a VLAN instance, specify a VLAN ID with the bridge slot/port
path cost command when the switch is running in the 1x1 mode. For example, the following command
configures a 16-bit path cost value for port 8/1 for VLAN 10 to 19 (the port speed is 100 MB, 19 is the
recommended value).
-> bridge 10 8/1 path cost 19
The explicit bridge 1x1 slot/port path cost command configures the port path cost value for a VLAN
instance when the switch is running in either mode (1x1 or flat). For example, the following command
performs the same function as the command in the previous example:
-> bridge 1x1 10 8/1 path cost 19
To change the port path cost value for the flat mode instance, use either the bridge slot/port path cost
command or the bridge cist slot/port path cost command. Note that both commands are available when
the switch is running in either mode (1x1 or flat) and an instance number is not required. For example, the
following commands configure a 32-bit path cost value for port 1/24 for the flat mode instance to 20,000
(the port speed is 1 GB, 20,000 is the recommended value):
-> bridge 1/24 path cost 20000
-> bridge cist 1/24 path cost 20000
As in previous releases, it is possible to configure the flat mode instance with the bridge slot/port path
cost command by specifying 1 as the instance number (e.g., bridge 1 1/24 path cost 19). However, this is
only available when the switch is already running in the flat mode and STP or RSTP is the active protocol.
The port path cost value is also configurable for a Multiple Spanning Tree Instance (MSTI). To configure
this value for an MSTI, use the explicit bridge msti slot/port path cost command and specify the MSTI
ID for the instance number. For example, the following command configures the path cost value for port
1/12 for MSTI 10 to 19:
-> bridge msti 10 1/12 path cost 19
Note that when MSTP is the active flat mode protocol, explicit Spanning Tree bridge commands are
required to configure parameter values. Implicit commands are for configuring parameters when the STP
or RSTP protocols are in use. See Chapter 2, “Using 802.1Q 2005 Multiple Spanning Tree,” for more
information.
Path Cost for Link Aggregate Ports
Physical ports that belong to a link aggregate do not participate in the Spanning Tree Algorithm. Instead,
the algorithm is applied to the aggregate logical link (virtual port) that represents a collection of physical
ports. By default, Spanning Tree is enabled on the aggregate logical link and the path cost value is set to
zero.
If a 32-bit path cost value is in use and the path_cost for a link aggregate is set to zero, the following
default values based on link speed and link aggregate size are used:
Link Speed
Aggregate Size
(number of links)
Default Path
Cost Value
10 MB 2 1,200,000
4 800,000
8 600,000
100 MB 2 120,000
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