Portfast

Sections:

Overview:

Port-Fast enables a switch port to accelerate the time it takes to transition to the forwarding state
Enabling Port-Fast on ports allows the switchports to bypass the listening and learning states of the STP forward delay timers
The goal of Port-Fast is to enable end user devices to connect to the network almost instantly improving the user experience

When to use:

PortFast is recommended for access ports connected to devices like computers, printers, or other non-switch devices that don’t have the ability to cause loops by forwarding BPDUs
PortFast should never be enabled on switch to switch links as this could lead to Spanning Tree loops and inconsistencies on the network

Portfast Configuration

Scenario1 - Without Portfast

Scenario:

Intention is to shutdown the Gi3/3 port on AccessSW1 towards the client PC in VLAN20
Re-enabling the port will transition to the forwarding state after going through the Spanning Tree timers
As you can see, clients on the network will have to wait for these timers to expire before being able to send any traffic on the network
Default 802.1D Spanning Tree Timers:
- Listening State: 15sec
- Learning State: 15sec
- Overall: 30sec until the client can send traffic

Scenario2 - Portfast Configuration

Scenario:

Intention for this lab scenario is to enable Portfast on the Gi3/3 port on AccessSW1 towards the client PC in VLAN20
As you can see, clients on the network are able to send traffic on the network almost immediately bypassing the Listening and Learning forward delay timers of the Spanning Tree protocol

Spanning Tree