Configuring STP Port Parameters Configuring Spanning Tree Parameters
page 6-38 OmniSwitch AOS Release 7 Network Configuration Guide June 2013
configures 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):
-> spantree cist port 1/24 path-cost 20000
The port path cost value is also configurable for a Multiple Spanning Tree Instance (MSTI). To configure
this value for an MSTI, use the spantree msti 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:
-> spantree msti 10 port 1/12 path-cost 19
Note that configuring the port path cost value for a MSTI is allowed in both modes (per-VLAN and flat)
only when the Spanning Tree protocol is set to MSTP.
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. Spanning Tree is automatically enabled on the aggregate logical link and the path cost value is set to
the default value.
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:
If a 16-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. Note that for Gigabit ports the aggre-
gate size is not applicable in this case:
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
480,000
860,000
1 GB 2 12,000
48,000
86,000
10 GB 2 1,200
4800
8600
Link Speed
Aggregate Size
(number of links)
Default Path
Cost Value
10 Mbps 2 60
440
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