What is Cisco Portfast?

Asked By: Brayan Hernandez | Last Updated: 3rd April, 2020
Category: technology and computing computer networking
3.9/5 (238 Views . 25 Votes)
Portfast shortens/bypasses normal STP timers to get ports up and forwarding as quickly as practical. This typically is a host PC/Workstation. It's used to minimimize the impact of STP TCN BPDU traffic when a simple host is being rebooted or connected to a switch. It's a Layer 2 function so routers/firewalls are out.

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In this regard, what is PortFast used for?

Enabling the PortFast feature causes a switch or a trunk port to enter the STP forwarding-state immediately or upon a linkup event, thus bypassing the listening and learning states. The PortFast feature is enabled at a port level, and this port can either be a physical or a logical port.

Subsequently, question is, how do I enable PortFast on a Cisco switch? First, you need to select an interface for which you want to enable or configure PortFast, and then execute the spanning-tree portfast command to enable this feature. As shown in the preceding figure, the PortFast feature will only have effect when the interface is in a non-trunking mode.

Likewise, people ask, is PortFast enabled by default?

PortFast is not enabled by default. With PortFast enabled on a port, you effectively take the port and tell spanning tree not to implement STP on that port.

Is PortFast Cisco proprietary?

Portfast is a Cisco proprietary solution to deal with spanning-tree topology changes. A switch will never generate a topology change notification for an interface that has portfast enabled.

33 Related Question Answers Found

What is a Bpdu packet?

BPDU - bridge protocol data unit
BPDUs are data messages that are exchanged across the switches within an extended LAN that uses a spanning tree protocol topology. BPDU packets contain information on ports, addresses, priorities and costs and ensure that the data ends up where it was intended to go.

How do I check my PortFast status?

To view the configured Spanning Tree PortFast enabled ports, run the "show running-config" IOS command as shown below. We can see that PortFast is enabled on access ports fa0/1 to fa0/24. To display a detailed summary of interface information, run "show spanning-tree detail" command as shown below.

What does Bpdu stand for?

bridge protocol data unit

How do I stop a Cisco switch from STP?

The spanning tree feature cannot be turned off in switches on a per port basis. Although it is not recommended, you can turn off Spanning Tree Protocol (STP) on a per-VLAN basis, or globally on the switch. Use the no spanning-tree vlan vlan-id command in order to disable STP on a per virtual LAN (VLAN) basis.

How do I configure Portfast?


Configure the Spanning-Tree portfast Setting
  1. Enter the configuration mode for the interface.
  2. Shut down the interface.
  3. Change the portfast setting.
  4. Review the portfast status.
  5. Reset the default spanning tree portfast value for the interface.
  6. Review the portfast status.

What is Portfast and Bpdu guard?

PortFast BPDU guard prevents loops by moving a nontrunking port into an errdisable state when a BPDU is received on that port. When you enable BPDU guard on the switch, spanning tree shuts down PortFast-configured interfaces that receive BPDUs instead of putting them into the spanning tree blocking state.

Can we use spanning Portfast on trunk ports?

The PortFast feature is enabled at a port level, and this port can either be a physical or a logical port. When PortFast feature is enabled on a switch or a trunk port, the port immediately transitions to the STP forwarding state. Though PortFast is enabled the port still participates in STP.

Does Portfast disable spanning tree?

A common misunderstanding among Cisco students is that portfast disables spanning-tree on a certain interface. This is not correct however…if you enable portfast on an interface then it will jump to the forwarding state of spanning-tree.

Should spanning tree be enabled on all ports?

Not configuring spanning tree at all
As I said, spanning tree is a good thing. But for some reason, a lot of switch vendors disable it by default. So out of the box, you might have to enable the protocol. You configure the command “spanning-tree portfast” on all the ports connecting to end devices like workstations.

How can I check my Bpdu Guard status?


Displaying the BPDU guard status. To display the BPDU guard state, enter the show running configuration or the show stp-bpdu-guard command. For the BPDU status enter the stp-bpdu-guard command.

What is STP networking?

The Spanning Tree Protocol (STP) is a network protocol that builds a loop-free logical topology for Ethernet networks. The basic function of STP is to prevent bridge loops and the broadcast radiation that results from them.

What is Spanning Tree PortFast Bpduguard default?

Explanation. At the global level, you can enable BPDU filtering on Port Fast-enabled interfaces by using the spanning-tree portfast bpdufilter default global configuration command. This command prevents interfaces that are in a Port Fast-operational state from sending or receiving BPDUs.

Why is Cisco Port err disabled?

Errdisable is a feature that automatically disables a port on a Cisco Catalyst switch. When a port is error disabled, it is effectively shut down and no traffic is sent or received on that port. The error disabled feature is supported on most Catalyst switches running the Cisco IOS software.

What happens if a Portfast port receives a Bpdu?

Answer: If a Portfast enabled port receives BPDUs it will lose its Portfast status, regardless if configured on interface or globally. If it has the command on it and you shut/no shut then I assume that any state is lost and it would do what the config says which is to bring the port into forwarding immediately.

What is root guard?


The root guard feature of Cisco switches is designed to provide a way to enforce the placement of root bridges in the network. Root guard limits the switch ports out of which the root bridge may be negotiated.

What is UplinkFast STP?

UplinkFast is a Cisco specific feature that improves the convergence time of the Spanning-Tree Protocol (STP) in the event of the failure of an uplink. The UplinkFast feature is supported on Cisco Catalyst 4500/4000, 5500/5000, and 6500/6000 series switches running CatOS.

What is Switchport host?

Cisco -- switchport host
Use the switchport host interface configuration command on the switch stack or on a standalone switch to optimize a Layer 2 port for a host connection. This command does 3 things!