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PT Activity 5.5.

2: Challenge Spanning Tree Protocol

Topology Diagram

Addressing Table

Device Interface IP Address Subnet Mask Default Gateway

S1 VLAN 99 172.17.99.11 255.255.255.0 N/A
S2 VLAN 99 172.17.99.12 255.255.255.0 N/A
S3 VLAN 99 172.17.99.13 255.255.255.0 N/A
PC1 NIC 172.17.10.21 255.255.255.0 172.17.10.12
PC2 NIC 172.17.20.22 255.255.255.0 172.17.20.12
PC3 NIC 172.17.30.23 255.255.255.0 172.17.30.12

Port Assignments – S2

Ports Assignment Network

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

Introduction In this activity. 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.. subnet mask. and PC3 with the IP address. check for missing configuration statements. PC2.. and S3 switches according to the following guidelines and save all your configurations: Configure the switch hostname as indicated on the topology. examine the Spanning Tree Protocol and learn how to optimize it. • Configure VLANs. Page 2 of 11 . you will perform basic switch configurations. Task 2: Configure the Ethernet Interfaces on the Host PCs From the Desktop tab. If not. configure VLANs. All contents are Copyright © 1992–2007 Cisco Systems. CCNA Exploration LAN Switching and Wireless: STP PT Activity 5. • Configure spanning tree. Inc.2: Challenge Spanning Tree Protocol Learning Objectives • Perform basic switch configurations. [OK] Your completion results should be 18 percent. This document is Cisco Public Information. End with CNTL/Z. • Configure a password of cisco for vty connections. • Configure an encrypted privileged EXEC mode password of class. If not. • Optimizing STP. configure addressing on PCs.5. S2. All rights reserved. one per line. • Configure the Ethernet interfaces on the host PCs. use the IP Configuration window to configure the Ethernet interfaces of PC1. • Configure a password of cisco for console connections. Task 1: Perform Basic Switch Configurations Configure the S1. • Disable DNS lookup. Your completion results should be 26 percent. check for missing configuration steps. and gateway indicated in the addressing table. Switch>enable Switch#configure terminal Enter configuration commands.

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

Only the commands for the FastEthernet0/1 interface on each switch are shown. Configure trunking ports and native VLAN. This document is Cisco Public Information. configure ports Fa0/1 through Fa0/5 as trunking ports. Designate VLAN 99 as the native VLAN for these trunks.5. Page 4 of 11 . When this activity was started. Verify the VLANs. Configure Trunk Links and Native VLAN. Inc. This ensures consistency in the VLAN configuration across the network. these ports were disabled and must be re-enabled now using the no shutdown command. Configure the VTP server with VLANs.CCNA Exploration LAN Switching and Wireless: STP PT Activity 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 4.2: Challenge Spanning Tree Protocol Step 3. but the commands should be applied up to the FastEthernet0/5 interface. S2#show vlan brief All contents are Copyright © 1992–2007 Cisco Systems. For each switch. Configure the following VLANS on the VTP server: VLAN VLAN Name VLAN 99 management VLAN 10 faculty-staff VLAN 20 students VLAN 30 guest S1(config)#vlan 99 S1(config-vlan)#name management S1(config)#vlan 10 S1(config-vlan)#name faculty-staff S1(config)#vlan 20 S1(config-vlan)#name students S1(config)#vlan 30 S1(config-vlan)#name guest S1(config-vlan)#end Step 5. VTP allows you to configure VLANs on the VTP server and have those VLANs populated to the VTP clients in the domain. Use the show vlan brief command on S2 and S3 to verify that all four VLANs have been distributed to the client switches. All rights reserved.

Fa0/8. Fa0/4. All rights reserved. Fa0/19.255. Page 5 of 11 .5. Fa0/7. From S1. Step 7.11 255.99. Fa0/12.0 Verify that the switches are correctly configured by pinging between them. This document is Cisco Public Information. 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 ---.255. Fa0/11. Fa0/9 Fa0/10.255.99. However.----------------------------- 1 default active Fa0/1. Fa0/23. Fa0/12. Assign switch ports to the VLANs. Fa0/16. S1(config)#interface vlan99 S1(config-if)#ip address 172.Fa0/13 Fa0/14. Fa0/7. Fa0/11.255.17. Fa0/2. Fa0/9 Fa0/10.11 does not support the interface range command. Fa0/8.Fa0/17 Fa0/18.----------------------------- 1 default active Fa0/1.Fa0/21 Fa0/22.17.-------------------------------. Inc.0 S3(config)#interface vlan99 S3(config-if)#ip address 172. Fa0/5 Fa0/6.--------.-------------------------------. Fa0/15.Fa0/17 Fa0/18.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5. only assign the first port from each range. Fa0/24.13 255. Fa0/24. since Packet Tracer 4.--------.99.255. Fa0/19. Fa0/20.17. ping the management interface on S2 and S3.255. Fa0/4. Fa0/23.Fa0/21 Fa0/22. Fa0/16.12 255. 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. Configure the management interface address on all three switches. ping the management interface on S3. Gi0/1 Gi0/2 1002 fddi-default active 1003 token-ring-default active 1004 fddinet-default active 1005 trnet-default active Step 6. From S2. Were the pings successful? If not. Fa0/5 Fa0/6.0 S2(config)#interface vlan99 S2(config-if)#ip address 172. Fa0/2. troubleshoot the switch configurations and try again. Port assignments are listed in the table at the beginning of the activity.2: Challenge Spanning Tree Protocol VLAN Name Status Ports ---. Fa0/20.Fa0/13 Fa0/14. Fa0/15.

3 Shr Fa0/2 Altn BLK 19 128. This document is Cisco Public Information.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 Shr Fa0/3 Desg FWD 19 128. Inc.146E Aging Time 300 Interface Role Sts Cost Prio. -------------------------------- Fa0/1 Root FWD 19 128. ---.Nbr Type ---------------.F20D. display the spanning tree table with the show spanning-tree command.146E Aging Time 300 Interface Role Sts Cost Prio. The output is shown for S1 only.5.3 Shr VLAN0020 Spanning tree enabled protocol ieee Root ID Priority 32788 Address 0030. Examine the default configuration of 802.3 Shr Fa0/2 Altn BLK 19 128. -------.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.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. All rights reserved. In this activity S3 is currently the root.Nbr Type ---------------.1D Spanning Tree Protocol (STP).0F68. --------.3 Shr Fa0/4 Desg FWD 19 128.3 Shr Fa0/4 Desg FWD 19 128.3 Shr Fa0/3 Desg FWD 19 128.3 Shr VLAN0010 Spanning tree enabled protocol ieee Root ID Priority 32778 Address 0030.. Root selection varies depending on the default BID of each switch. --. On each switch. --------. Page 6 of 11 . ---. [OK] S2# Your completion results should be 99 percent. --. Task 4: Configure Spanning Tree Step 1. S1#show spanning-tree VLAN0001 Spanning tree enabled protocol ieee Root ID Priority 32769 Address 0030. CCNA Exploration LAN Switching and Wireless: STP PT Activity 5. -------------------------------- Fa0/1 Root FWD 19 128.F20D.2: Challenge Spanning Tree Protocol Destination filename [startup-config]? [enter] Building configuration. -------. If not..F20D.0F68. check for missing configuration statements.

3 Shr VLAN0099 Spanning tree enabled protocol ieee Root ID Priority 32867 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.F20D. Page 7 of 11 .2: Challenge Spanning Tree Protocol Address 0050. Inc.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. -------.3 Shr Note that there are five instances of STP on each switch.3 Shr Fa0/2 Altn BLK 19 128. -------.Nbr Type ---------------.146E Aging Time 300 All contents are Copyright © 1992–2007 Cisco Systems. 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 0030.146E Aging Time 300 Interface Role Sts Cost Prio.146E Aging Time 300 Interface Role Sts Cost Prio. -------------------------------- Fa0/1 Root FWD 19 128.F20D. This document is Cisco Public Information.3 Shr Fa0/2 Altn BLK 19 128.0F68.F20D. ---.0F68. -------------------------------- Fa0/1 Root FWD 19 128.3 Shr Fa0/2 Altn BLK 19 128. --. --.3 Shr Fa0/4 Desg FWD 19 128.146E Aging Time 300 Interface Role Sts Cost 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 Shr VLAN0030 Spanning tree enabled protocol ieee Root ID Priority 32798 Address 0030.5.3 Shr Fa0/3 Desg FWD 19 128. ---. All rights reserved.0F68.Nbr Type ---------------.3 Shr Fa0/4 Desg FWD 19 128. --.0F68.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5.3 Shr Fa0/3 Desg FWD 19 128. --------. --------. -------------------------------- Fa0/1 Root FWD 19 128.Nbr Type ---------------.3 Shr Fa0/4 Desg FWD 19 128.3 Shr Fa0/3 Desg FWD 19 128. -------.

--. What is the priority for switches S1.3 Shr Step 2.7258 Aging Time 300 Interface Role Sts Cost Prio. --.3 Shr Fa0/2 Altn BLK 19 128.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5. ---. and 99? ______________________________________________________________________________ All contents are Copyright © 1992–2007 Cisco Systems. -------------------------------- Fa0/1 Root FWD 19 128. Examine the output.3 Shr S2#show spanning-tree vlan 99 VLAN0099 Spanning tree enabled protocol ieee Root ID Priority 32867 Address 0030.3 Shr Fa0/3 Desg FWD 19 128.5. 30. All rights reserved. Answer the following questions based on the output. -------.Nbr Type ---------------. -------.F20D.3 Shr Fa0/3 Desg FWD 19 128. ---.Nbr Type ---------------. -------------------------------- Fa0/1 Root FWD 19 128. --------. S2.3 Shr Fa0/4 Desg FWD 19 128. Page 8 of 11 . 20.2: Challenge Spanning Tree Protocol Interface Role Sts Cost Prio.D6B1 Aging Time 300 Interface Role Sts Cost Prio.Nbr Type ---------------.F20D. and S3 on VLAN 99? ______________________________________________________________________________ What is the priority for S1 on VLANs 10. Inc.3 Shr Fa0/3 Altn BLK 19 128.3 Shr S3#show spanning-tree vlan 99 VLAN0099 Spanning tree enabled protocol ieee Root ID Priority 32867 Address 0030. --. --------.3 Shr Fa0/2 Altn BLK 19 128.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.F7AE. This document is Cisco Public Information. ---.F20D. -------------------------------- Fa0/1 Desg FWD 19 128. -------.3 Shr Fa0/2 Desg FWD 19 128. --------.3 Shr Fa0/4 Desg FWD 19 128.3 Shr Fa0/4 Altn BLK 19 128.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.

1D and is the focal point for spanning tree control traffic. as you have observed. the same root is elected for every spanning tree. Because the root can be defined on the basis of the VLAN. The default priority. Ideally the root is in the distribution layer.5. S3#show spanning-tree vlan 99 VLAN0099 Spanning tree enabled protocol ieee Root ID Priority 4195 Address 0050. In the example output below. Set the priority for VLAN 99 on S1 to 4096. If the default switch priorities are used in root selection. • The placement of the root defines the active switched paths in the network. Inc. only two are carrying traffic. the default root switch for all VLANs is S3. as we have seen. This document is Cisco Public Information. Therefore. is 32768 plus the VLAN ID. All rights reserved. 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. • Consider the topology used in this activity.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 root switch must be capable of handling this additional load. it has been determined that the root selection using default values has led to under- utilization of the available switch trunks. CCNA Exploration LAN Switching and Wireless: STP PT Activity 5. This could lead to an inferior design. Some reasons to control the selection of the root switch include: • The root switch is responsible for generating BPDUs in STP 802. a separate root election is conducted for each instance. Page 9 of 11 .0F68.146E 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. you can have some ports blocking for one VLAN and forwarding for another. Of the six trunks configured. Random placement is likely to lead to suboptimal paths. it is a waste of resources. While this prevents loops. Selection of the root switch is accomplished by changing the spanning-tree priority for the VLAN. In this example. The lower number indicates a higher priority for root selection. This is demonstrated below. it is necessary to force another switch to become the root switch for VLAN 99 to impose some load-sharing on the trunks. 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).

Inc.F20D. -------------------------------- Fa0/4 Desg FWD 19 128.Nbr Type ---------------.146E Aging Time 300 Interface Role Sts Cost Prio.-------. -------------------------------- Fa0/4 Desg FWD 19 128. ---.146E Aging Time 300 Interface Role Sts Cost Prio.D6B1 Aging Time 300 Interface Role Sts Cost Prio.---. --. --------.3 Shr All contents are Copyright © 1992–2007 Cisco Systems.2: Challenge Spanning Tree Protocol Address 0030.3 Shr Fa0/1 Desg FWD 19 128.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 Shr S1#show spanning-tree vlan 99 VLAN0099 Spanning tree enabled protocol ieee Root ID Priority 4195 Address 0050. -------.0F68. S1#show spanning-tree vlan 10 VLAN0010 Spanning tree enabled protocol ieee Root ID Priority 32778 Address 0030. Page 10 of 11 . ---.-------------------------------- Fa0/4 Desg FWD 19 128. --------. --.3 Shr Fa0/3 Desg FWD 19 128.Nbr Type ---------------.3 Shr Fa0/2 Altn BLK 19 128.5.3 Shr Fa0/3 Desg FWD 19 128.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5.146E 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.F20D.0F68. All rights reserved.3 Shr Fa0/2 Desg FWD 19 128. -------.--------.--.0F68.3 Shr Fa0/1 Root FWD 19 128.3 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.Nbr Type ---------------. This document is Cisco Public Information.

Page 11 of 11 . If not.3 Shr Fa0/2 Altn BLK 19 128. By configuring groups of VLANs to use different trunks as their primary forwarding path.CCNA Exploration LAN Switching and Wireless: STP PT Activity 5.2: Challenge Spanning Tree Protocol Fa0/3 Desg FWD 19 128. without having to leaves trunks totally unused. with one of four S1 ports in blocking mode.3 Shr Fa0/1 Root FWD 19 128.5. use Check Results to find any incomplete components. the original spanning tree topology. Your completion results should be 100 percent. we retain the redundancy of failover trunks. All rights reserved. However.3 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. Inc. All contents are Copyright © 1992–2007 Cisco Systems. is still in place for the four other active VLANs. This document is Cisco Public Information.