Lab 70: Configuring Spanning Tree Protocol for Access Ports (PortFast)

Lab Objective:

The objective of this lab exercise is to configure access ports to transition immediately to the Forwarding state, instead of going through the typical Spanning Tree states (i.e., Blocking, Listening, Learning, etc.).

Lab Purpose:

Bypassing default Spanning Tree port states is a fundamental skill. By default, it can take up to 60 seconds for a switchport to transition to the Forwarding state and begin forwarding frames. In most cases, this is acceptable; however, on a network with DHCP clients, for example, that need IP addressing information from a DHCP server, this duration may cause these clients to think that the DHCP server is unavailable.

Certification Level:

This lab is suitable for both ICND2 and CCNA certification exam preparation.

Lab Difficulty:

This lab has a difficulty rating of 4/10.

Readiness Assessment:

When you are ready for your certification exam, you should complete this lab in no more than 10 minutes.

Lab Topology:

Please use any single switch for this lab. This lab is strictly about validating command syntax.

Task 1:

Configure a hostname of your liking on your switch, which should have at least 12 ports.

Task 2:

Configure VLAN10 named SALES on the switch.

Task 3:

Configure ports FastEthernet0/1 and FastEthernet0/2 using the interface range command so that Spanning Tree Protocol transitions these interfaces into a Forwarding state immediately. These interfaces should also be configured as access ports in VLAN10.

Task 4:

Verify your configuration using the appropriate commands in Cisco IOS.

Configuration and Verification

Task 1:

For reference information on configuring hostnames, please refer to earlier labs.

Task 2:

For reference information on configuring and verifying VLANs, please refer to earlier labs.

Task 3:

Sw1#conf t 
Enter configuration commands, one per line.  End with CTRL/Z. 
Sw1(config)#interface range fastethernet0/1 - 2 
Sw1(config-if-range)#switchport mode access 
Sw1(config-if-range)#switchport access vlan10 
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 2 interfaces due to the range command but will only have effect when the interfaces are in a non-trunking mode. 

Task 4:

Sw1#show spanning-tree interface fastethernet 0/2 detail 
Port 2 (FastEthernet0/2) of VLAN0010 is forwarding 
 Port path cost 100, Port priority 128, Port Identifier 128.2.
 Designated root has priority 4106, address 000d.bd06.4100 
 Designated bridge has priority 4106, address 000d.bd06.4100 
 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    
The port is in the portfast mode 
 Link type is shared by default 
 BPDU: sent 81, received 0

The command above won’t work on Packet Tracer so use a show run instead if you don’t have access to a live switch.


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