How to configure and verify Spanning Tree Protocol (STP) PortFast

PortFast is a feature which can be used to speed up convergence on ports which are connected to a workstation or a server (which will not cause layer 2 loops).

• To configure Spanning Tree Protocol (STP) PortFast on a Switch running IOS, run "spanning-tree portfast" command as shown below.

omnisecu.com.SW1>enable
omnisecu.com.SW1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
omnisecu.com.SW1(config)#interface range fa0/1 - 20
omnisecu.com.SW1(config-if-range)#switchport mode access
omnisecu.com.SW1(config-if-range)#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 will be configured in 20 interfaces due to the range command
 but will only have effect when the interfaces are in a non-trunking mode.
omnisecu.com.SW1(config-if-range)#exit
omnisecu.com.SW1(config)#exit

%SYS-5-CONFIG_I: Configured from console by console
omnisecu.com.SW1#

• 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.

omnisecu.com.SW1#show running-config
Building configuration...

Current configuration : 2003 bytes
!
version 12.2
no service timestamps log datetime msec
no service timestamps debug datetime msec
no service password-encryption
!
hostname omnisecu.com.SW1
!
!
spanning-tree mode pvst
!
interface FastEthernet0/1
 switchport mode access
 spanning-tree portfast
!
interface FastEthernet0/2
 switchport mode access
 spanning-tree portfast
!
interface FastEthernet0/3
 switchport mode access
 spanning-tree portfast
!
interface FastEthernet0/4
 switchport mode access
 spanning-tree portfast
!
interface FastEthernet0/5
 switchport mode access
 spanning-tree portfast
!
interface FastEthernet0/6
 switchport mode access
 spanning-tree portfast
!
<output omitted>

• To display a detailed summary of interface information, run "show spanning-tree detail" command as shown below.

omnisecu.com.SW1#show spanning-tree detail 

VLAN0001 is executing the ieee compatible Spanning Tree Protocol
  Bridge Identifier has priority of 32768, sysid 1, 00E0.A333.3C56
  Configured hello time 2, max age 20, forward delay 15
  Current root has priority 32769
  Topology change flag not set, detected flag not set
  Number of topology changes 0 last change occurred 00:00:00 ago
	        from FastEthernet0/1
  Times:  hold 1, topology change 35, notification 2
  		hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 0, notification 0, aging 300

Port 1 (FastEthernet0/1) of VLAN0001 is designated forwarding
  Port path cost 19, Port priority 128, Port Identifier 128.1
  Designated bridge has priority 32769, address 00E0.A333.3C56
  Designated port id is 128.1, designated path cost 19
  Timers: message age 16, forward delay 0, hold 0
  Number of transitions to forwarding state: 1
  Link type is point-to-point by default
  <output omitted>

• To display Spanning Tree information on active interfaces only, run "show spanning-tree active" IOS command as shown below.

omnisecu.com.SW1#show spanning-tree active 
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     00E0.A333.3C56
             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     00E0.A333.3C56
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  20

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1            Desg FWD 19        128.1    P2p
Gi1/2            Desg FWD 4         128.26   P2p
Fa0/2            Desg FWD 19        128.2    P2p
Fa0/3            Desg FWD 19        128.3    P2p
Fa0/4            Desg FWD 19        128.4    P2p
Fa0/5            Desg FWD 19        128.5    P2p
Fa0/6            Desg FWD 19        128.6    P2p
Fa0/7            Desg FWD 19        128.7    P2p
Fa0/8            Desg FWD 19        128.8    P2p
Fa0/9            Desg FWD 19        128.9    P2p