Configuring The Pvst+ Default Port Cost Mode; Configuring The Pvst+ Port Vlan Cost - Cisco WS-C2950SX-48-SI Configuration Manual

Using PVST+
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Configuring the PVST+ Default Port Cost Mode

If any switch in your network is using a port speed of 10 Gb or over and the network is using PVST+
spanning tree mode, all switches in the network must have the same path cost defaults. You can enter
the set spantree defaultcostmode command to force all VLANs associated with all the ports to have
the same pathcost default set.
There are two default port cost modes available–short and long.
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The default port cost mode in PVST+ is short. For port speeds of 10 Gb and greater, you must set the
default port cost mode to long.
To change the default port cost mode, perform this task in privileged mode:
Task
Configure the default port cost mode.
This example shows how to configure the default port cost mode:
Console> (enable) set spantree defaultcostmode long
Portcost and portvlancost set to use long format default values.
Console> (enable)

Configuring the PVST+ Port VLAN Cost

You can configure the port cost for a port on a per-VLAN basis. Ports with a lower port VLAN cost are
more likely to be chosen to forward frames. You should assign lower numbers to ports that are attached
to faster media (such as full duplex) and higher numbers to ports that are attached to slower media. The
default cost differs for different media.
You can set a cost value from 1– 65535.
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide
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Vlan Port-State
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The short mode has these parameters:
Portcost.
–
Portvlancost.
–
– When you enable UplinkFast, the actual cost is incremented by 3000.
The long mode has these parameters:
– Portcost.
– Portvlancost.
– When you enable UplinkFast, the actual cost is incremented by 10,000,000.
EtherChannel computes the cost of a bundle using the formula,
–
AVERAGE_COST/NUM_PORT.
Cost
not-connected 4
not-connected 4
not-connected 100
not-connected 100
forwarding 19
not-connected 100
Command
set spantree defaultcostmode {short | long}
Chapter 7 Configuring Spanning Tree
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Release 8.1
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