You are on page 1of 11

PT Activity 5.5.

2: Challenge Spanning Tree Protocol
Topology Diagram

Addressing Table
Device S1 S2 S3 PC1 PC2 PC3 Interface VLAN 99 VLAN 99 VLAN 99 NIC NIC NIC IP Address 172.17.99.11 172.17.99.12 172.17.99.13 172.17.10.21 172.17.20.22 172.17.30.23 Subnet Mask 255.255.255.0 255.255.255.0 255.255.255.0 255.255.255.0 255.255.255.0 255.255.255.0 Default Gateway N/A N/A N/A 172.17.10.12 172.17.20.12 172.17.30.12

Port Assignments – S2
Ports Fa0/1 - 0/5 Fa0/6 - 0/10 Fa0/11 - 0/17 Fa0/18 - 0/24 Assignment 802.1q Trunks (Native VLAN 99) VLAN 30 – Guest(Default) VLAN 10 – Faculty/Staff VLAN 20 - Students Network 172.17.99.0 /24 172.17.30.0 /24 172.17.10.0 /24 172.17.20.0 /24

All contents are Copyright © 1992–2007 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information.

Page 1 of 11

• • • • Disable DNS lookup. check for missing configuration statements. Configure a password of cisco for console connections.2: Challenge Spanning Tree Protocol Learning Objectives • • • • • Perform basic switch configurations. you will perform basic switch configurations. check for missing configuration steps.5. and PC3 with the IP address. use the IP Configuration window to configure the Ethernet interfaces of PC1. Configure the Ethernet interfaces on the host PCs.. This document is Cisco Public Information. and gateway indicated in the addressing table.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5. Your completion results should be 26 percent. one per line.. If not. If not. Configure VLANs. Inc. configure addressing on PCs. All contents are Copyright © 1992–2007 Cisco Systems. End with CNTL/Z. PC2. Optimizing STP. Configure an encrypted privileged EXEC mode password of class. Switch(config)#hostname S1 S1(config)#enable secret class S1(config)#no ip domain-lookup S1(config)#line console 0 S1(config-line)#password cisco S1(config-line)#login S1(config-line)#line vty 0 15 S1(config-line)#password cisco S1(config-line)#login S1(config-line)#end %SYS-5-CONFIG_I: Configured from console by console S1#copy running-config startup-config Destination filename [startup-config]? Building configuration. Configure a password of cisco for vty connections. Introduction In this activity. Switch>enable Switch#configure terminal Enter configuration commands. Task 1: Perform Basic Switch Configurations Configure the S1. configure VLANs. and S3 switches according to the following guidelines and save all your configurations: Configure the switch hostname as indicated on the topology. Task 2: Configure the Ethernet Interfaces on the Host PCs From the Desktop tab. examine the Spanning Tree Protocol and learn how to optimize it. Configure spanning tree. All rights reserved. [OK] Your completion results should be 18 percent. S2. Page 2 of 11 . subnet mask.

5.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5. Refer to the topology diagram to determine which switch ports on S2 are activated for end-user device access. S2(config)#interface fa0/6 S2(config-if)#switchport mode access S2(config-if)#no shutdown S2(config-if)#interface fa0/11 S2(config-if)#switchport mode access S2(config-if)#no shutdown S2(config-if)#interface fa0/18 S2(config-if)#switchport mode access S2(config-if)#no shutdown Step 2. Page 3 of 11 . Switch Name S1 S2 S3 VTP Operating Mode Server Client Client VTP Domain Lab5 Lab5 Lab5 VTP Password cisco cisco cisco S1(config)#vtp mode server Device mode already VTP SERVER. S1(config)#vtp domain Lab5 Changing VTP domain name from NULL to Lab5 S1(config)#vtp password cisco Setting device VLAN database password to cisco S1(config)#end S2(config)#vtp mode client Setting device to VTP CLIENT mode S2(config)#vtp domain Lab5 Changing VTP domain name from NULL to Lab5 S2(config)#vtp password cisco Setting device VLAN database password to cisco S2(config)#end S3(config)#vtp mode client Setting device to VTP CLIENT mode S3(config)#vtp domain Lab5 Changing VTP domain name from NULL to Lab5 S3(config)#vtp password cisco Setting device VLAN database password to cisco S3(config)#end All contents are Copyright © 1992–2007 Cisco Systems. Inc. Enable the user ports on S2 in access mode. Configure VTP on the three switches using the following table. This document is Cisco Public Information. All rights reserved. The default operating mode is server. Configure VTP.2: Challenge Spanning Tree Protocol Task 3: Configure VLANs Step 1. Remember that VTP domain names and passwords are case-sensitive. These three ports will be configured for access mode and enabled with the no shutdown command.

Verify the VLANs. Inc. All rights reserved. Configure the following VLANS on the VTP server: VLAN VLAN 99 VLAN 10 VLAN 20 VLAN 30 S1(config)#vlan 99 S1(config-vlan)#name S1(config)#vlan 10 S1(config-vlan)#name S1(config)#vlan 20 S1(config-vlan)#name S1(config)#vlan 30 S1(config-vlan)#name S1(config-vlan)#end Step 5. but the commands should be applied up to the FastEthernet0/5 interface. When this activity was started. Configure the VTP server with VLANs. This ensures consistency in the VLAN configuration across the network. VTP allows you to configure VLANs on the VTP server and have those VLANs populated to the VTP clients in the domain. Designate VLAN 99 as the native VLAN for these trunks. For each switch.2: Challenge Spanning Tree Protocol Step 3. Only the commands for the FastEthernet0/1 interface on each switch are shown. these ports were disabled and must be re-enabled now using the no shutdown command. configure ports Fa0/1 through Fa0/5 as trunking ports. S2#show vlan brief All contents are Copyright © 1992–2007 Cisco Systems. Page 4 of 11 VLAN Name management faculty-staff students guest management faculty-staff students guest .CCNA Exploration LAN Switching and Wireless: STP PT Activity 5.5. S1(config)#interface fa0/1 S1(config-if)#switchport mode trunk S1(config-if)#switchport trunk native vlan 99 S1(config-if)#no shutdown S1(config)#end S2(config)#interface fa0/1 S2(config-if)#switchport mode trunk S2(config-if)#switchport trunk native vlan 99 S2(config-if)#no shutdown S2(config-if)#end S3(config)#interface fa0/1 S3(config-if#switchport mode trunk S3(config-if)#switchport trunk native vlan 99 S3(config-if)#no shutdown S3(config-if-#end Step 4. This document is Cisco Public Information. Configure trunking ports and native VLAN. Use the show vlan brief command on S2 and S3 to verify that all four VLANs have been distributed to the client switches. Configure Trunk Links and Native VLAN.

Gi0/1 Gi0/2 10 faculty/staff active 20 students active 30 guest active 99 management active S3#show vlan brief VLAN Name Status Ports ---. Fa0/9 Fa0/10.----------------------------1 default active Fa0/1.-------------------------------. Fa0/24. only assign the first port from each range. Fa0/2. Fa0/8.Fa0/21 Fa0/22.255. ping the management interface on S3. Fa0/16. Page 5 of 11 . Fa0/5 Fa0/6.12 255.Fa0/21 Fa0/22.0 S3(config)#interface vlan99 S3(config-if)#ip address 172. Fa0/11.--------. All rights reserved. Assign switch ports to the VLANs. Configure the management interface address on all three switches. This document is Cisco Public Information. From S2. since Packet Tracer 4.Fa0/13 Fa0/14.0 Verify that the switches are correctly configured by pinging between them. Fa0/19.99.0 S2(config)#interface vlan99 S2(config-if)#ip address 172.--------. ping the management interface on S2 and S3.17.255. Gi0/1 Gi0/2 1002 fddi-default active 1003 token-ring-default active 1004 fddinet-default active 1005 trnet-default active Step 6.255.17.255.2: Challenge Spanning Tree Protocol VLAN Name Status Ports ---. Fa0/23. Inc. Fa0/4.----------------------------1 default active Fa0/1. Fa0/16.11 255. From S1. S1(config)#interface vlan99 S1(config-if)#ip address 172. Fa0/4.255.99. Fa0/9 Fa0/10.17.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5. Fa0/7.255.Fa0/17 Fa0/18. Fa0/11. Fa0/20. Fa0/15.Fa0/17 Fa0/18. Fa0/12. Fa0/24. However. Were the pings successful? If not. Fa0/15. Step 7.Fa0/13 Fa0/14. Fa0/2. Fa0/5 Fa0/6. troubleshoot the switch configurations and try again. Fa0/7. Fa0/19.99. S2(config)#interface fa0/6 S2(config-if)#switchport access vlan 30 S2(config-if)#interface fa0/11 S2(config-if)#switchport access vlan 10 S2(config-if)#interface fa0/18 S2(config-if)#switchport access vlan 20 S2(config-if)#end S2#copy running-config startup-config All contents are Copyright © 1992–2007 Cisco Systems. Fa0/12.11 does not support the interface range command.5. Port assignments are listed in the table at the beginning of the activity. Fa0/8. Fa0/23. Fa0/20.-------------------------------.13 255.

In this activity S3 is currently the root..D6B1 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32788 (priority 32768 sys-id-ext 20) All contents are Copyright © 1992–2007 Cisco Systems. Page 6 of 11 .3 128.3 128.3 128.F20D.. Task 4: Configure Spanning Tree Step 1. display the spanning tree table with the show spanning-tree command.3 Type -------------------------------Shr Shr Shr Shr VLAN0010 Spanning tree enabled protocol ieee Root ID Priority 32778 Address 0030.0F68. All rights reserved.3 128.Nbr -------128.146E Aging Time 300 Interface ---------------Fa0/1 Fa0/2 Fa0/3 Fa0/4 Role ---Root Altn Desg Desg Sts --FWD BLK FWD FWD Cost --------19 19 19 19 Prio. Root selection varies depending on the default BID of each switch. S1#show spanning-tree VLAN0001 Spanning tree enabled protocol ieee Root ID Priority 32769 Address 0030.F20D.D6B1 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32769 (priority 32768 sys-id-ext 1) Address 0050.3 Type -------------------------------Shr Shr Shr Shr VLAN0020 Spanning tree enabled protocol ieee Root ID Priority 32788 Address 0030.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5.0F68.D6B1 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32778 (priority 32768 sys-id-ext 10) Address 0050.146E Aging Time 300 Interface ---------------Fa0/1 Fa0/2 Fa0/3 Fa0/4 Role ---Root Altn Desg Desg Sts --FWD BLK FWD FWD Cost --------19 19 19 19 Prio.3 128.F20D. On each switch. [OK] S2# Your completion results should be 99 percent. The output is shown for S1 only. This document is Cisco Public Information. If not. Inc.5.1D Spanning Tree Protocol (STP).2: Challenge Spanning Tree Protocol Destination filename [startup-config]? [enter] Building configuration.Nbr -------128.3 128. check for missing configuration statements. Examine the default configuration of 802.

3 128.146E Aging Time 300 Interface ---------------Fa0/1 Fa0/2 Fa0/3 Fa0/4 Role ---Root Altn Desg Desg Sts --FWD BLK FWD FWD Cost --------19 19 19 19 Prio.D6B1 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32867 (priority 32768 sys-id-ext 99) Address 0050.3 128.2: Challenge Spanning Tree Protocol Address 0050.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5.3 Type -------------------------------Shr Shr Shr Shr VLAN0030 Spanning tree enabled protocol ieee Root ID Priority 32798 Address 0030.D6B1 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32867 (priority 32966 sys-id-ext 99) Address 0050. Inc.3 128.0F68.0F68.3 Type -------------------------------Shr Shr Shr Shr VLAN0099 Spanning tree enabled protocol ieee Root ID Priority 32867 Address 0030.F20D.3 128. Page 7 of 11 .D6B1 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32798 (priority 32768 sys-id-ext 30) Address 0050.F20D.Nbr -------128.0F68.3 128. Examine the VLAN 99 spanning tree for all three switches: S1#show spanning-tree vlan 99 VLAN0099 Spanning tree enabled protocol ieee Root ID Priority 32867 Address 0030.Nbr -------128.146E Aging Time 300 Interface ---------------Fa0/1 Fa0/2 Fa0/3 Fa0/4 Role ---Root Altn Desg Desg Sts --FWD BLK FWD FWD Cost --------19 19 19 19 Prio.0F68.3 128.3 Type -------------------------------Shr Shr Shr Shr Note that there are five instances of STP on each switch.146E Aging Time 300 Interface ---------------Fa0/1 Fa0/2 Fa0/3 Fa0/4 Role ---Root Altn Desg Desg Sts --FWD BLK FWD FWD Cost --------19 19 19 19 Prio. All rights reserved.5.F20D.146E Aging Time 300 All contents are Copyright © 1992–2007 Cisco Systems.3 128.3 128.Nbr -------128. This document is Cisco Public Information.3 128.

3 128.D6B1 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32867 (priority 32966 sys-id-ext 99) Address 00E0.3 128. Examine the output. What is the priority for switches S1. Page 8 of 11 . Inc.2: Challenge Spanning Tree Protocol Interface ---------------Fa0/1 Fa0/2 Fa0/3 Fa0/4 Role ---Root Altn Desg Desg Sts --FWD BLK FWD FWD Cost --------19 19 19 19 Prio.F20D. and 99? ______________________________________________________________________________ All contents are Copyright © 1992–2007 Cisco Systems.D6B1 Aging Time 300 Interface ---------------Fa0/1 Fa0/2 Fa0/3 Fa0/4 Role ---Desg Desg Desg Desg Sts --FWD FWD FWD FWD Cost --------19 19 19 19 Prio.3 128.3 Type -------------------------------Shr Shr Shr Shr Step 2.3 128.3 128. This document is Cisco Public Information.3 Type -------------------------------Shr Shr Shr Shr S3#show spanning-tree vlan 99 VLAN0099 Spanning tree enabled protocol ieee Root ID Priority 32867 Address 0030.Nbr -------128.3 128.F7AE. Answer the following questions based on the output. S2.5. 20. All rights reserved.Nbr -------128.3 128.F20D.F20D.3 128.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5.7258 Aging Time 300 Interface ---------------Fa0/1 Fa0/2 Fa0/3 Fa0/4 Role ---Root Altn Altn Altn Sts --FWD BLK BLK BLK Cost --------19 19 19 19 Prio.3 128.Nbr -------128. and S3 on VLAN 99? ______________________________________________________________________________ What is the priority for S1 on VLANs 10.D6B1 This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32867 (priority 32966 sys-id-ext 99) Address 0030. 30.3 Type -------------------------------Shr Shr Shr Shr S2#show spanning-tree vlan 99 VLAN0099 Spanning tree enabled protocol ieee Root ID Priority 32867 Address 0030.

Page 9 of 11 . In the example output below. The placement of the root defines the active switched paths in the network. Random placement is likely to lead to suboptimal paths. Of the six trunks configured. Ideally the root is in the distribution layer. as you have observed. This could lead to an inferior design. S1(config)#spanning-tree vlan 99 priority 4096 S1(config)#exit Give the switches a little time to recalculate the spanning tree and then check the tree for VLAN 99 on switch S3 (the original VLAN 99 root) and switch S1 (the non-root switch selected to become the new VLAN 99 root). you can have some ports blocking for one VLAN and forwarding for another.146E Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32867 (priority 32966 sys-id-ext 99) All contents are Copyright © 1992–2007 Cisco Systems.1D and is the focal point for spanning tree control traffic. Therefore. it is a waste of resources. the default root switch for all VLANs is S3. Some reasons to control the selection of the root switch include: • • • The root switch is responsible for generating BPDUs in STP 802. is 32768 plus the VLAN ID. In this example. Consider the topology used in this activity. Selection of the root switch is accomplished by changing the spanning-tree priority for the VLAN.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5. as we have seen. S3#show spanning-tree vlan 99 VLAN0099 Spanning tree enabled protocol ieee Root ID Priority 4195 Address 0050. The root switch must be capable of handling this additional load.5.2: Challenge Spanning Tree Protocol Which ports are blocking VLAN 99 on the root switch? ______________________________________________________________________________ Which ports are blocking VLAN 99 on the non-root switches? ______________________________________________________________________________ How does STP select the root? ______________________________________________________________________________ Since the bridge priorities are all the same. The default priority. All rights reserved. This document is Cisco Public Information. While this prevents loops. it is necessary to force another switch to become the root switch for VLAN 99 to impose some load-sharing on the trunks. only two are carrying traffic. Inc. the same root is elected for every spanning tree. it has been determined that the root selection using default values has led to underutilization of the available switch trunks. This is demonstrated below. a separate root election is conducted for each instance. what else does the switch use to determine the root? ______________________________________________________________________________ Task 5: Optimizing STP Because there is a separate instance of the spanning tree for every active VLAN. Because the root can be defined on the basis of the VLAN. The lower number indicates a higher priority for root selection. If the default switch priorities are used in root selection.0F68. Set the priority for VLAN 99 on S1 to 4096.

This document is Cisco Public Information. Page 10 of 11 .3 128.D6B1 Aging Time 300 Interface ---------------Fa0/4 Fa0/1 Fa0/2 Fa0/3 Role ---Desg Root Altn Desg Sts --FWD FWD BLK FWD Cost --------19 19 19 19 Prio. Inc.---.5.Nbr -------128.3 128.-------------------------------Fa0/4 Desg FWD 19 128.2: Challenge Spanning Tree Protocol Address 0030.--------.0F68.146E Aging Time 300 Interface Role Sts Cost Prio.146E This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 4195 (priority 4294 sys-id-ext 99) Address 0050. S1#show spanning-tree vlan 10 VLAN0010 Spanning tree enabled protocol ieee Root ID Priority 32778 Address 0030.3 128.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5.D6B1 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32778 (priority 32788 sys-id-ext 10) Address 0050.3 Type -------------------------------Shr Shr Shr Shr S1#show spanning-tree vlan 99 VLAN0099 Spanning tree enabled protocol ieee Root ID Priority 4195 Address 0050.-------.3 128.146E Aging Time 300 Interface ---------------Fa0/4 Fa0/3 Fa0/2 Fa0/1 Role ---Desg Desg Desg Desg Sts --FWD FWD FWD FWD Cost --------19 19 19 19 Prio.Nbr Type ---------------.F20D.--.0F68.Nbr -------128.F20D.3 Shr All contents are Copyright © 1992–2007 Cisco Systems.3 Type -------------------------------Shr Shr Shr Shr Which switch is the root for VLAN 99? ______________________________________________________________________________ Which ports are blocking VLAN 99 traffic on the new root? ______________________________________________________________________________ Which ports are now blocking VLAN 99 traffic on the old root? ______________________________________________________________________________ Compare the S1 VLAN 99 spanning tree above with the S1 VLAN 10 spanning tree.3 128.0F68.3 128. All rights reserved.

is still in place for the four other active VLANs. we retain the redundancy of failover trunks. without having to leaves trunks totally unused. Inc.3 128.5. This document is Cisco Public Information.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5. By configuring groups of VLANs to use different trunks as their primary forwarding path. Page 11 of 11 .3 128. Your completion results should be 100 percent. with one of four S1 ports in blocking mode. If not. All contents are Copyright © 1992–2007 Cisco Systems. use Check Results to find any incomplete components. the original spanning tree topology.2: Challenge Spanning Tree Protocol Fa0/3 Fa0/2 Fa0/1 Desg FWD 19 Altn BLK 19 Root FWD 19 128. However. All rights reserved.3 Shr Shr Shr Note that S1 can now use all four ports for VLAN 99 traffic as long as they are not blocked at the other end of the trunk.