How the Multi-Chassis role works

Anytime a switch with the Multi-Chassis role is set to active, the switch performs the STP operation. The switch with the role set to standby relays the information to the switch with the active role for STP tasks.

The show spanning-tree vlan <VLAN-ID> detail command provides information about the value of the Multi-Chassis role.

Example of the Multi-Chassis role with the active value:

switch# show spanning-tree vlan 2 detail

VLAN2
Spanning tree status : Enabled Protocol: RPVST
  Root ID    Priority   : 32768
             MAC-Address: 54:80:28:fd:45:00
             Hello time(in seconds):2  Max Age(in seconds):20
             Forward Delay(in seconds):15

  Bridge ID  Priority  : 32768
             MAC-Address: 54:80:28:fd:78:00
             Hello time(in seconds):2  Max Age(in seconds):20
             Forward Delay(in seconds):15

Port         Role           State        Cost           Priority   Type
------------ -------------- ------------ ------------ ---------- ----------
lag2         Designated     Forwarding   2000           64         point_to_point
lag100       Designated     Forwarding   1              64         point_to_point
lag110       Root           Forwarding   2000           64         point_to_point

Topology change flag          : False
Number of topology changes    : 122
Last topology change occurred : 4 seconds ago

Port lag1
Designated root has priority               :32768 Address: 54:80:28:fd:45:00
Designated bridge has priority             :32768 Address: 54:80:28:fd:d7:00
Designated port                            : 322
Multi-Chassis role                         :active
Number of transitions to forwarding state  :42
Bpdus sent 510, received 96

Port lag100
Designated root has priority               :32768 Address: 54:80:28:fd:45:00
Designated bridge has priority             :32768 Address: 54:80:28:fd:d7:00
Designated port                            : 420
Number of transitions to forwarding state  :41
Bpdus sent 536, received 46

Example of the Multi-Chassis role with the active value:

switch# show spanning-tree vlan 2 detail

VLAN2
Spanning tree status : Enabled Protocol: RPVST
  Root ID    Priority   : 32768
             MAC-Address: 54:80:28:fd:45:00
             Hello time(in seconds):2  Max Age(in seconds):20
             Forward Delay(in seconds):15

  Bridge ID  Priority  : 32768
             MAC-Address: 54:80:28:fd:78:00
             Hello time(in seconds):2  Max Age(in seconds):20
             Forward Delay(in seconds):15

Port         Role           State        Cost           Priority   Type
------------ -------------- ------------ ------------ ---------- ----------
lag2         Disabled       Forwarding   4              64         point_to_point
lag100       Root           Forwarding   1              64         point_to_point
lag110       Disabled       Forwarding   4              64         point_to_point

Topology change flag          : False
Number of topology changes    : 1
Last topology change occurred : 804 seconds ago

Port lag1
Designated root has priority               : 0 Address:
Designated bridge has priority             : 0 Address:
Designated port                            :(null)
Multi-Chassis role                         :standby
Number of transitions to forwarding state  : 0
Bpdus sent 0, received 0

Port lag100
Designated root has priority               :32768 Address: 54:80:28:fd:45:00
Designated bridge has priority             :32768 Address: 54:80:28:fd:77:ff
Designated port                            : 420
Number of transitions to forwarding state  : 2
Bpdus sent 110, received 529