What are PortFast, BPDU Guard and BPDU Filter You Must Know About it.

In this article, You will know about 

  • what Is Demerits of STP has Face Cisco?
  • What is PortFast, BPDU Guard, BPDU Filter Uplinkfast and BackboneFast?
  • How to Configure All above Protocol in the switch?

What Needs to do to Reduce Convergence Time.

STP Provides a loop-free network but takes a longer time (nearly 50 seconds) for convergence. This is very high in networking terms. In most cases, this is a critical issue, especially for important network services like VoIP, servers etc.

BPDU Guard, Bpdu filter, Uplinkfast,  Backbonefast,
Switch With PortFast Enable

To deal with this challenge, Cisco has added the following features to the STP implementation on Its switches

  • PortFast, BPDU Guard and BPDU Filter 
  • UplinkFast ‘
  • BackboneFast


How does this work?

If there is a computer or a server connected to a switch port, then there is no necessity to listen to the BPDUs as it is not a Layer-2 device.

 Loops will not be created as it has a single link to the Layer-2 network. Therefore, the advantage is that the Spanning Tree on such ports can be disabled.

When a switch port is configured as Portfast, STP is disabled on that port. The port will not be blocked and will transition to the forwarding state when it comes up in the queue. ‘

The command for configuring portfast is spanning-tree portfast ’.

Observe that in the following figure the server is connected in the Fastethemet 0/1
on switch 1, Hence, there is no requirement to run spanning-tree on Fa0/1. The portfast is enabled on Fa0/1, displayed as below:

SW1# config  t
Enter configuration commands, one per line. End with CNTL/Z.
SW1 (config) interface fa0/1
Sw1 (config-if) spanning-tree portfast.
Warning: portfast should only be enabled on ports connected to a single host. Connecting hubs, concentrators, switches, bridges, etc… To this interface when portfast is enabled,  can cause temporary bridging loops.
Use with CAUTION

%Portfast has been configured on FastEthernet0/1 but Will only have effect when the interface is in a non-trunking mode.

This usually skips listening and learning state and ups the link to the forwarding state. 

Also Read;

BPDU Guard


Consider this situation.

If a switch is plugged into a switchport configured as Portfast (that is planned to connect computers or servers), it could change the STP topology without the knowledge of the administrator. It could even bring down the network!

To protect this, BPDU Guard can be configured on the switchport using the command

‘Switch (config-if) # spanning-tree bpduguard enable.

This command must be configured only on your access layer switches, or switches where users are directly connected.


An entrance layer switch which has redundant uplink linking with 2 distribution layer switches. Normally, one uplink could be in the Forwarding state so the other could be in the Blocking state.

If the essential uplink went down, around 50 secs could pass by before the repetitive uplink could be utilized. 

By the help of UplinkFast on Cisco switches leaf-hub switches or potentially switches at the closures of the spanning tree limbs to have a working root port keeping up more than one of the excess or potential root ports in Blocking mode. 

Whenever the essential root port uplink falls flat, another blocked uplink in a split second can be raised for use.

To configure Uplinkfast  use the following command:

Switch(config)# spanning-tree uplinkfast 


In the backbonefast, an entirely unexpected strategy would be utilized to abbreviate STP combination. 

BackboneFast works by having a switch effectively decide if elective ways are accessible to the root bridge, in the occasion the switch distinguishes an indirect connection disappointment.

 Indirect connection disappointments happen when a connection which isn’t straightforwardly associated with a switch comes up short. 

A switch recognizes a roundabout connection disappointment whenever it gets second rate BPDUs from its assigned bridge on the two its own one of a kind root port or a blocked port.( Inferior BPDUs are sent from an assigned bridge that has lost its connection with the root bridge, which influences it to proclaim itself as the new root)

To configure the BackboneFast  use the following command:
Switch(config)# spanning-tree backbonefast