In a network, the spanning tree protocol (STP) is super important. It stops loops, which can mess up things like broadcast storms. It uses clever math to create a loop-free setup for Ethernet networks. To keep an eye on it, network admins use different show commands. In this article, we’ll check out some common show commands that tell us about the STP protocol setup and how it’s doing.
After configuring the Spanning Tree Protocol, which is usually configured on Layer 2 Switches, it may be necessary to verify the settings made. When configuring Cisco Switches, we typically use the CLI command prompt.
What are the Show Commands of the STP (Spanning Tree Protocol) We Use in Cisco Switches?
After configuring STP, we can learn which Switch is a Root Bridge or which Switch is a blocked port with CLI commands. In addition, we can examine PortFast, UplinkFast, and BackboneFast features with these commands.
Create a redundancy network using the GNS3 or Cisco Packet Tracer program and apply the following commands on Switch Privileged Mode to examine what operations the ST is doing.
1. Spanning-Tree ? Command
This command shows the show commands of the ST protocol supported on the Switch. You can check its outputs by selecting the feature you want to use from the commands listed with the command.
Switch#show spanning-tree ?
WORD bridge group list, example 1,3-5,7,9
active Report on active interfaces only
backbonefast Show spanning tree backbonefast status
blockedports Show blocked ports
bridge Status and configuration of this bridge
detail Detailed information
inconsistentports Show inconsistent ports
interface Spanning Tree interface status and configuration
mst Multiple spanning trees
pathcost Show Spanning pathcost options
root Status and configuration of the root bridge
summary Summary of port states
uplinkfast Show spanning tree uplinkfast status
vlan VLAN Switch Spanning Trees
| Output modifiers
Switch#show spanning-tree
2. Spanning-Tree Command
With this command, you can view general information about the ST protocol on the Switch. You can view the Root ID, Root Bridge, and Interface ports of the Switch and view the port states of the Switch’s interfaces.
Also, if Root Bridge is configured manually, you can examine the Switch’s Priority value using this command.
Switch#show spanning-tree
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0012.6620.0800
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0012.6620.0800
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/0 Desg FWD 4 128.1 Shr
Gi0/1 Desg FWD 4 128.2 Shr
Gi0/2 Desg FWD 4 128.3 Shr
Gi0/3 Desg FWD 4 128.4 Shr
Switch#
3. Summary Command
With this command, you can view the connection status of VLANs created on Cisco Switch. You can also view the features enabled by the Standard STP (PVST) protocol with this command. If you have performed the BackboneFast configuration, you can view the information about the BackboneFast feature with this command.
It displays the connection status for VLANs created on the Cisco Switch. You can also view the activated properties of the PVST with this command. If you have performed the configuration steps, you can view the BackboneFast feature information with this command.
Switch#show spanning-tree summary
Switch is in pvst mode
Root bridge for: VLAN0001
Extended system ID is enabled
Portfast Default is disabled
PortFast BPDU Guard Default is disabled
Portfast BPDU Filter Default is disabled
Loopguard Default is disabled
EtherChannel misconfig guard is enabled
Configured Pathcost method used is short
UplinkFast is disabled
BackboneFast is disabled
Name Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
VLAN0001 0 0 0 4 4
---------------------- -------- --------- -------- ---------- ----------
1 vlan 0 0 0 4 4
Switch#
4. Root Command
You can view Root Bridge information with this command. For example, when you apply this command on a Switch that is not Root Bridge, you can see the Root Bridge ID and Address (0012.66b3.c800).
Switch#show spanning-tree root
Root Hello Max Fwd
Vlan Root ID Cost Time Age Dly Root Port
---------------- -------------------- --------- ----- --- --- ------------
VLAN0001 32769 0012.6620.0800 0 2 20 15
Switch#
5. Detail Command
With this command, you can see detailed information on all ports of the Switch. You can view the Priority and Root Bridge information of the Cisco Switch interfaces, Hello Time, Max Age Timer, and Forward Delay times, as well as the number of BPDU packets sent and received.
Switch#show spanning-tree detail
VLAN0001 is executing the ieee compatible Spanning Tree protocol
Bridge Identifier has priority 32768, sysid 1, address 0012.6620.0800
Configured hello time 2, max age 20, forward delay 15
We are the root of the spanning tree
Topology change flag not set, detected flag not set
Number of topology changes 1 last change occurred 00:25:15 ago
from GigabitEthernet0/0
Times: hold 1, topology change 35, notification 2
hello 2, max age 20, forward delay 15
Timers: hello 1, topology change 0, notification 0, aging 300
Port 1 (GigabitEthernet0/0) of VLAN0001 is designated forwarding
Port path cost 4, Port priority 128, Port Identifier 128.1.
Designated root has priority 32769, address 0012.6620.0800
Designated bridge has priority 32769, address 0012.6620.0800
Designated port id is 128.1, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is shared by default
BPDU: sent 773, received 3
Port 2 (GigabitEthernet0/1) of VLAN0001 is designated forwarding
Port path cost 4, Port priority 128, Port Identifier 128.2.
Designated root has priority 32769, address 0012.6620.0800
Designated bridge has priority 32769, address 0012.6620.0800
Designated port id is 128.2, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is shared by default
BPDU: sent 771, received 0
Port 3 (GigabitEthernet0/2) of VLAN0001 is designated forwarding
Port path cost 4, Port priority 128, Port Identifier 128.3.
Designated root has priority 32769, address 0012.6620.0800
Designated bridge has priority 32769, address 0012.6620.0800
Designated port id is 128.3, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is shared by default
BPDU: sent 771, received 0
Port 4 (GigabitEthernet0/3) of VLAN0001 is designated forwarding
Port path cost 4, Port priority 128, Port Identifier 128.4.
Designated root has priority 32769, address 0012.6620.0800
Designated bridge has priority 32769, address 0012.6620.0800
Designated port id is 128.4, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is shared by default
BPDU: sent 773, received 3
Switch#6. Show Spanning-Tree Interface Command
It is used to examine the interfaces on the device with this command.
The interfaces you want to select are displayed in the following command output. After selecting the interface you wish to view, you can see the interface states as the output below.
Switch#show spanning-tree interface ?
GigabitEthernet GigabitEthernet IEEE 802.3z
Multilink Multilink-group interface
Port-channel Ethernet Channel of interfaces
Vlan Catalyst Vlans
Switch#show spanning-tree interface gigabitethernet 0/0
Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0001 Desg FWD 4 128.1 Shr
Switch#show spanning-tree interface gigabitethernet 0/1
Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0001 Desg FWD 4 128.2 Shr
Switch#
7. Show Spanning-Tree Blocked
With this command, you can see the interfaces that are put into Blocked Mode. In short, it shows the ports blocked by STP.
Switch#show spanning-tree blockedports
Name Blocked Interfaces List
-------------------- ------------------------------------
Number of blocked ports (segments) in the system : 0
Switch#8. Show Spanning-Tree Active
This command shows only the interfaces that are active on the Cisco Switch. For example, if the idle-free interfaces are closed by the system administrator, you will be able to view only the functional interfaces with this command.
Switch#show spanning-tree active
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0012.6620.0800
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0012.6620.0800
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/0 Desg FWD 4 128.1 Shr
Gi0/1 Desg FWD 4 128.2 Shr
Gi0/2 Desg FWD 4 128.3 Shr
Gi0/3 Desg FWD 4 128.4 Shr
Switch#
9. Spanning-Tree Bridge
This command shows the Bridge ID information of the Cisco Switch.
Switch#show spanning-tree bridge
Hello Max Fwd
Vlan Bridge ID Time Age Dly Protocol
---------------- --------------------------------- ----- --- --- --------
VLAN0001 32769 (32768, 1) 0012.6620.0800 2 20 15 ieee
Switch#
10. Spanning-Tree Inconsistentports
This command displays ports that are not configured correctly in the configuration. For example, if one port Trunk between two interconnected Switches is configured as an Access port, the STP protocol will name this port inconsistently.
Switch#show spanning-tree inconsistentports
Name Interface Inconsistency
-------------------- ------------------------ ------------------
Number of inconsistent ports (segments) in the system : 0
Switch#
11. BackboneFast Command
This command shows whether the BackboneFast feature is enabled on the Switch.
Switch#show spanning-tree backbonefast
BackboneFast is disabled
Switch#
12. UplinkFast Command
This command shows whether the UplinkFast feature is enabled on the Switch.
Switch#show spanning-tree uplinkfast
UplinkFast is disabled
Switch#
13. Vlan Command
Finally, you can view STP details such as Root ID, Root Bridge, and Priority according to the VLAN number selected with this command.
Switch#sh spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0012.6620.0800
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0012.6620.0800
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/0 Desg FWD 4 128.1 Shr
Gi0/1 Desg FWD 4 128.2 Shr
Gi0/2 Desg FWD 4 128.3 Shr
Gi0/3 Desg FWD 4 128.4 Shr
Switch#Conclusion
For troubleshooting in Cisco Switch or Routers, we need to know and understand the commands in detail. In this article, we have examined the basic commands of the ST protocol. Thanks for following us!
TolgaBagci
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