portfast and uplinkfast

1 Boson NetSim Lab Manual

SWITCH Lab: PortFast and UplinkFast

ObjectiveCon gure PortFast and UplinkFast. PortFast is an option that allows a switchport to change from blocking to

forwarding immediately upon detection of a link. If PortFast is disabled, it will take up to 60 seconds for the port

to forward. This sometimes causes applications, such as Dynamic Host Con guration Protocol (DHCP), to fail.

P1PC1 and P2PC2 are PC workstations. P1ASW1 and P2ASW2 are Access layer switches. P1DSW1 and

P2DSW2 are Distribution layer switches. The Access and Distribution layers are two of the three layers in the

Cisco three-layer hierarchical network model, which also includes the Core layer.

Lab TopologyThe Topology diagram below represents the NetMap in the Simulator:

P2DSW2

P2ASW2P1ASW1

P1DSW1

P1PC1 P2PC2

VLAN 11 VLAN 12

VLAN 1 172.16.1.10

VLAN 11 172.16.11.10VLAN 1 172.16.1.20

VLAN 12 172.16.12.20

VLAN 1 172.16.1.100

VLAN 11 172.16.11.100VLAN 1 172.16.1.200

VLAN 12 172.16.12.200

Lab ID: 8.8K412A132.SWP.1


Command Summary

Command Description

interface type number changes from global con guration mode to interface con guration

mode

ping ip-address sends an Internet Control Message Protocol (ICMP) echo request

to the speci ed address

show spanning-tree vlan vlan-id shows whether spanning tree is running for a virtual LAN (VLAN)

shutdown; no shutdown disables an interface; enables an interface

spanning-tree portfast enables portfast

spanning-tree uplinkfast sets UplinkFast

switchport access vlan vlan-id assigns the default VLAN for a port

switchport mode {access | dynamic

{auto | desirable} | trunk}

con gures the VLAN membership mode of a port

switchport trunk encapsulation dot1q con gures trunk for 802.1Q encapsulation

Lab Tasks

Task 1: Con gure PortFast and UplinkFast

1. Ping from P1PC1 to P1ASW1 (172.16.11.10). The ping should succeed.

2. On P1ASW1, shut down the FastEthernet 0/5 port, which connects to P1PC1. Wait 5 seconds, and then

re-enable the port. While Spanning Tree Protocol (STP) is recalculating, quickly try another ping from

P1PC1 to P1ASW1. Notice that the ping now fails.

3. Wait about 40 seconds to ensure that STP has nished calculating, and then try the ping again. Does the

ping succeed? ______________________________________________________________________

4. On P1ASW1, enable PortFast on the FastEthernet 0/5 port, which connects to P1PC1.


5. On P1ASW1, disable and enable the FastEthernet 0/5 port. Immediately after enabling the port, try to

ping P1ASW1 from P1PC1. How long does it take for the ping to succeed this time? _______________

6. On P1DSW1, con gure FastEthernet ports 0/1 and 0/2 as trunking ports.

7. Determine which of the ports that connect from P1ASW1 to P1DSW1 are blocking for VLAN 11.

8. Verify that you can ping from P1PC1 to P1DSW1 (172.16.11.100).

9. On P1ASW1, disable the forwarding port for VLAN 11. While STP is recalculating, quickly try another

ping from P1PC1 to P1DSW1 (172.16.11.100). Notice that the ping now fails. How long does STP take to

reconverge? ________________________________________________________________________

10. On P1ASW1, enable UplinkFast port and then enable the FastEthernet 0/1 interface.

11. Verify that you can ping from P1PC1 to P1DSW1 (172.16.11.100).

12. From P1ASW1, disable the forwarding port for VLAN 11. Immediately attempt to ping from P1PC1 to

P1DSW1 (172.16.11.100). How long does STP take to reconverge? ____________________________

13. Re-enable the port. Immediately attempt to ping from P1PC1 to P1DSW1 (172.16.11.100). How long

does STP take to reconverge? _________________________________________________________


Lab Solutions

Task 1: Con gure PortFast and UplinkFast

1. On P1PC1, you should issue the ping 172.16.11.10 command to ping from P1PC1 to P1ASW1. The ping

should be successful.

2. On P1ASW1, you should issue the following commands to shut down the FastEthernet 0/5 port, which

connects to P1PC1:

P1ASW1(config)#interface fastethernet 0/5

P1ASW1(config-if)#shutdown

Wait 5 seconds, and then re-enable the port by issuing the following command:

P1ASW1(config-if)#no shutdown

Now, while STP is recalculating, quickly try another ping from P1PC1 to P1ASW1 by issuing the ping

172.16.11.10 command. Notice that the ping now fails.

3. After waiting about 40 seconds to ensure that STP has nished calculating, you should issue the ping

172.16.11.10 command again. The ping should succeed.

4. On P1ASW1, you should issue the following commands to enable PortFast on the FastEthernet 0/5 port,

which connects to P1PC1:


P1ASW1(config-if)#spanning-tree portfast

5. On P1ASW1, you should issue the following command to disable the FastEthernet 0/5 port:

P1ASW1(config-if)shutdown

Wait 5 seconds, and then re-enable the port by issuing the following command:

P1ASW1(config-if)no shutdown

After enabling the port, you should issue the ping 172.16.11.10 command from P1PC1 to ping P1ASW1.

The pings should succeed immediately.

6. On P1DSW1, you should issue the following commands to con gure FastEthernet ports 0/1 and 0/2 on

P1DSW1 as trunking ports in VLAN 11:

P1DSW1(config)#interface fastethernet 0/1

P1DSW1(config-if)#switchport trunk encapsulation dot1q

P1DSW1(config-if)#switchport mode trunk

P1DSW1(config-if)#interface fastethernet 0/2

P1DSW1(config-if)#switchport trunk encapsulation dot1q

P1DSW1(config-if)#switchport mode trunk


7. On P1ASW1, you should issue the show spanning-tree vlan 11 command to determine which of the

ports that connect to P1DSW1 are blocking for VLAN 11. Sample output is shown below:

P1ASW1#show spanning-tree vlan 11

VLAN0011

Spanning tree enabled protocol ieee

Root ID Priority 24567

Address 000C.1625.2062

Cost 38

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32768

Address 000C.3378.5283

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Uplinkfast enabled

Interface Port ID Designated Port ID

Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr

------------- -------- ------ --- ------- -------------------- --------

Fa0/1 128.1 19 FWD 19 24567 000C.1625.2062 128.1

Fa0/2 128.2 19 BLK 19 24567 000C.1625.2062 128.2

Fa0/3 128.3 19 BLK 38 24567 000C.1625.2062 128.3

Fa0/4 128.4 19 BLK 38 24567 000C.1625.2062 128.4

Fa0/5 128.5 19 FWD 0 32768 000C.3378.5283 0.5

8. On P1PC1, you should issue the ping 172.16.11.100 command to verify that you can ping P1DSW1.

9. From P1ASW1, issue the following commands to disable the forwarding port, which is the FastEthernet

0/1 interface, for VLAN 11:


P1ASW1(config-if)#shutdown

While STP is recalculating, you should issue the ping 172.16.11.100 command quickly to try another

ping from P1PC1 to P1DSW1. The ping should fail initially. Continue to issue the ping until it succeeds so

that you can observe how long it takes for Spanning Tree Protocol to reconverge. It should take about 30

seconds for STP to reconverge.

10. On P1ASW1, you should issue the following commands to globally enable UplinkFast and to enable the

FastEthernet 0/1 interface:

P1ASW1(config)#spanning-tree uplinkfast



11. On P1PC1, you should issue the ping 172.16.11.100 command to verify that you can ping P1DSW1.


12. From P1ASW1, you should issue the following commands to disable the forwarding port for VLAN:


P1ASW1(config-if)shutdown

On P1PC1, immediately issue the ping 172.16.11.100 command to attempt to ping P1DSW1. Observe

how long it takes for STP to reconverge. Convergence should occur immediately.

13. You should issue the following commands to re-enable the port.



On P1PC1, immediately issue the ping 172.16.11.100 command to attempt to ping P1DSW1. Observe

how long it takes for STP to reconverge. Convergence should occur immediately.


Sample Con guration Scripts

P1ASW1 P1ASW1 (continued)

P1ASW1#show running-config

!

Version 12.3

service timestamps debug uptime

service timestamps log uptime

no service password-encryption

!

hostname P1ASW1

ip cef

!

ip subnet-zero

spanning-tree uplinkfast

spanning-tree extend system-id

!

interface FastEthernet0/1

description P1ASW1 to P1DSW1

switchport mode trunk

!




!




!




!


description P1PC1 to P1ASW1

switchport mode access

switchport access vlan 11

spanning-tree portfast

!


switchport mode dynamic desirable

!



!



!



!



!



!



!

interface Vlan 1

ip address 172.16.1.10 255.255.255.0

no ip route-cache

!

interface Vlan0011

ip address 172.16.11.10 255.255.255.0

no ip route-cache

!

vlan 11 name 11

vlan 12 name 12

!

ip default-gateway 172.16.1.100

!

ip classless

no ip http server

!

line con 0

line aux 0

line vty 0 15

!

no scheduler allocate

end


Sample Con guration Scripts

P1DSW1 P1DSW1 (continued)

P1DSW1#show running-config

!

Version 12.3

service timestamps debug uptime

service timestamps log uptime

no service password-encryption

!

hostname P1DSW1

ip cef

!

ip subnet-zero

spanning-tree vlan 1 priority 24567

spanning-tree extend system-id

!


description P1DSW1 to P1ASW1

switchport trunk encapsulation dot1q


!





!





!





!


!


!


!


!


!


!


description P1DSW1 to P2DSW2



!


description P1DSW1 to P2DSW2



!

interface GigabitEthernet0/1

!

interface GigabitEthernet0/2

!

interface Vlan 1

ip address 172.16.1.100 255.255.255.0

no ip route-cache

!

interface Vlan0011

ip address 172.16.11.100 255.255.255.0

no ip route-cache

!

vlan 11 name 11

vlan 12 name 12

!

ip classless

no ip http server

!

line con 0

line aux 0

line vty 0 4

!

no scheduler allocate

end

Copyright 19962012 Boson Software, LLC. All rights reserved. NetSim software and documentation are protected by copyright law.

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