Configuring Restricted TCN

For setup, refer to Figure Spanning Tree Topology.

When a port is configured as Restricted TCN, the port will not process and propagate any topology change information received on the configured port. Enabling this configuration might result in temporary connectivity loss after changes in active spanning tree topology because of incorrect learnt station location information.

By default, the restricted-tcn feature is disabled.

In case of Provider Bridges, Restricted TCN will always be enabled on Customer Network Ports.

Execute the following commands to configure the Restricted TCN feature on the port.

Type the following:

  • Enter the Global Configuration Mode.
iS5comm# configure terminal
  • Enter the Interface Configuration Mode.
iS5comm(config)# interface gigabitethernet 0/1
  • Configure the restricted TCN feature.
iS5comm(config-if)# spanning-tree restricted-tcn
  • Return to the Privileged EXEC mode.
iS5comm(config-if)#end
  • View the spanning tree details.
iS5comm# show spanning-tree detail
Spanning tree Protocol Enabled.
MST00 is executing the mstp compatible Multiple Spanning Tree Protocol
Bridge Identifier has Priority 32768, Address 00:01:02:03:04:01
Configured  Max age 20 sec 0 cs,  Forward delay 15 sec 0 cs
Configured Hello Time 2 sec 0 cs
We are root of the spanning tree
Current Root has priority 32768, address  00:01:02:03:04:01
cost of root path is 200000
Number of Topology Changes 11, Time since topology Change 100 seconds ago
Transmit Hold-Count 3
Root Times : Max age 20 sec 0 cs     Forward delay 15 sec 0 cs
Port 1 [Gi0/1] of MST00 is Alternate     , Discarding
Gi0/1 is operating in the MSTP Mode
Port path cost  2000000, Port priority  128,
Port Identifier  128.1. Port HelloTime  2 sec 0 cs,
Timers: Hello - 0, Forward Delay - 0, Topology Change - 0
Designated root has priority 32768, address 00:01:02:03:04:01
Designated Bridge has priority 32768, address 00:01:02:03:04:01
Designated Port Id is 128.1, Designated pathcost is 0
Operational Forward delay 15 sec 0 cs, Max age 20 sec 0 cs
Number of Transitions to forwarding State : 7
PortFast is disabled
Link type is point to Point
BPDUs : sent 171, received 1000
Restricted Role is disabled.
Restricted TCN is enabled.
  • Execute the no spanning-tree restricted-tcn Interface Configuration mode command to disable the topology change guard/ restricted TCN feature on the port..
iS5comm(config-if) # no spanning-tree restricted-tcn