12-18
Catalyst 2950 Desktop Switch Software Configuration Guide
78-14982-01
Chapter 12 Configuring RSTP and MSTP
Configuring RSTP and MSTP Featur es

Configuring the Path Cost

The MSTP path cost default value is derived from the media speed of an interface. If a loop occurs, the
MSTP use s cost when se lecting an interfac e to put in the for warding st ate. You can assi gn lower cost
values to inter faces that you want selected firs t an d higher cost values that you wa nt sel ected last. If all
interf aces ha v e the same cost v a lue, the M STP puts the interf ace with th e lo west interf ace n umber in the
forwarding st at e an d b l ocks t he ot her in ter faces.
Beginning in privileged EXEC mode, follow these steps to configure the MSTP cost of an interface:
Note Th e show span ning-t ree mst interf ace interface-id privileged EXEC comma nd displays in formati on
only for por ts that are in a link-up ope rative state. Otherw ise, you can use the show running-config
privileged EX EC c omm and to con firm th e co nfigurat ion.
To return the interface to its default setting, use the no spanning-tree mst instance-id cost interface
configurati on comm a nd.
Command Purpose
Step 1 configure terminal Enter glob al co nfigur atio n mo de .
Step 2 interface interface-id Enter interface configuration mode, and specify an interface to
configure. Valid i nte rfaces i ncl ude p hysi cal p ort s an d por t
chan nels. Val id port-c hann el numbe rs are 1 to 6.
Step 3 spanning-tree mst instance-id cost cost Configure the cos t for an MST ins tance .
If a loop occurs, the MSTP uses the path cost when selecting an
interface to place into the forwarding state. A lower path cost
represe nts higher-speed tr ansmission .
For instance-id, the ra nge is 0 to 15 .
For cost, th e range is 1 to 2000000 00; the de fault value is
derived from the media speed of the interfac e.
Step 4 end Return to privileged EXEC mode.
Step 5 show spanning-tree mst interface interface-id
or
show spanning-tree mst instance-id
Verify your entries.
Step 6 copy running-config startup-config (Optional) Save your entries in the configuration file.