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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 12 Configuring RSTP and MSTP Configuring RSTP and MSTP Features

Configuring the Port Priority

If a loop occurs, the MSTP uses the port priority when selecting an interface to put into the forwarding
state. You can assign hig her priority v alues (lo wer numerical va lues) to in terf aces that yo u want selected
fi rst and lo wer priority v al ues (higher n umerical v al ues) that yo u want sel ected last . If all interfa ces hav e
the same p rior ity valu e, the M S TP pu ts th e int erf ac e wi th the lowe st inter f a ce number in the forwarding
state and blocks the other interfaces.
Beginning in privileged EXEC mode, follow these steps to configure the MSTP port priority 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 if the port is in a link-up operativ e state. Otherwise, you can use the show running-config interface
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 port-priority
interface configuration command.
Command Purpose
Step 1 configure terminal Enter glo bal co nfigur ati on mo de.
Step 2 interface interface-id Enter interfac e c onfigura tio n mode , and speci fy a n
interface to configure.
Valid in te rface s in clud e physic a l po rts a nd po rt c hann el s.
Valid port-channel numbers are 1 to 6.
Step 3 spanning-tree mst instance-id port-priority priority Configure the port priority for an MST instance.
For instance-id, the ra nge is 0 to 15 .
For priority, the ra nge is 0 to 25 5; t he de fault i s 128.
The lower the number, the higher the priority.
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.