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CCNPv7 SWITCH

Chapter 4-2 Lab – Multiple Spanning Tree
Topology

Objectives

Implement Multiple Spanning Tree

Leverage VTP version 3 with MST

Background
Cisco’s Per VLAN Spanning Tree (PVST) provides a significant step up from standard spanning tree in terms of
flexibility, allowing each VLAN to have its own independent spanning tree, thereby make better use of available
links in the network. A drawback to PVST is that there is an instance of PVST running for each VLAN in the
network, regardless of whether there are actually different spanning-tree topologies required. This presents the
potential for overwhelming the switch CPU and memory. Additionally, Cisco switches like those used in these labs
allow only a limited number of PVST instances – usually 128. If more than 128 VLANs are created, some of them
will not have any STP running, and therefore not have any switching loop protection. PVST and Rapid PVST are
simply unusable in that kind of environment. Lastly, PVST and Rapid PVST are Cisco-proprietary protocols and
generally unusable in mixed vendor environments.
Cisco was involved in the early development of Multiple Spanning Tree. MST was standardized as IEEE 802.1s in
2002 and merged into 802.1Q in 2005. MST is an open protocol derived from RSTP, sharing all its rapid
convergence properties, and in fact, the only standardized spanning-tree protocol for VLAN-based networks
supported by multiple vendors. MST is a compromise between common spanning-tree and per-VLAN spanning
tree. An MST instance represents a unique spanning-tree topology. Multiple MST instances can be created to
account for each of the required spanning-tree topologies in a network, and an arbitrary number of VLANs can be
mapped to a single MST instance.
In this lab you will set up two instances of MST, one for VLANs 99 and 100 and the other for VLANs 110 and 120.
All other VLANs will be mapped to the default MST instance (also referred to as IST or Internal Spanning Tree).

© 2014 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public.

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Page 2 of 12 .CFG running-config Destination filename [running-config]? 184 bytes copied in 0.403: %SYS-7-NV_BLOCK_INIT: Initialized the geometry of nvram *Mar 7 18:41:41.0(2)SE6 IP Services and LAN Base images.310 secs (594 bytes/sec) DLS1# Step 2: Configure Trunking Next configure interfaces F0/7 through F0/12 as 802.1Q trunk ports on all four switches. © 2014 Cisco and/or its affiliates. An example from DLS1: DLS1# tclsh reset. Catalyst 3650 switches (running any Cisco IOS XE release) and Catalyst 2960-Plus switches (running any comparable Cisco IOS image) can be used in place of the Catalyst 3560 switches and the Catalyst 2960 switches.tcl script you created in Lab 1 “Preparing the Switch” to set your switches up for this lab. configure all four switches VTP Servers.CCNPv7 SWITCH: Lab 4-2 – Multiple Spanning Tree Note: This lab uses Cisco Catalyst 3560 and 2960 switches running Cisco IOS 15. one per line. the commands available and output produced might vary from what is shown in this lab.output omitted> Would you like to enter the initial configuration dialog? [yes/no]: n Switch> en *Mar 1 00:01:30.CFG into the running-config with the command copy flash:BASE.915: %LINK-5-CHANGED: Interface Vlan1.tcl Erasing the nvram filesystem will remove all configuration files! Continue? [confirm] [OK] Erase of nvram: complete Reloading the switch in 1 minute. Reload Reason: Reload command. Required Resources  2 Cisco 2960 with the Cisco IOS Release 15. changed state to administratively down Switch# copy BASE.0(2)SE6 C3560-IPSERVICESK9-M or comparable  Computer with terminal emulation software  Ethernet and console cables Step 1: Prepare the switches for the lab Use the reset. Depending on the switch model and Cisco IOS Software version. respectively. Additionally.141: %SYS-5-RELOAD: Reload requested by console. Then load the file BASE. The 3560 and 2960 switches are configured with the SDM templates “dual-ipv4-andipv6 routing” and “lanbase-routing”. An example from DLS1: DLS1# conf t Enter configuration commands.CFG running-config. respectively. This document is Cisco Public.0(2)SE6 C2960-LANBASEK9-M or comparable  2 Cisco 3560v2 with the Cisco IOS Release 15. type reload cancel to halt Proceed with reload? [confirm] *Mar 7 18:41:40. All rights reserved. <switch reloads . DLS1(config)# vtp mode server End with CNTL/Z.

431: %SW_VLAN-6-VTP_DOMAIN_NAME_CHG: VTP domain name changed to SWLAB. An example from DLS1: DLS1#conf t Enter configuration commands. Issue the global configuration command spanning-tree mode mst and then the privileged exec command clear spanning-tree detected-protocols. End with CNTL/Z. DLS1(config)# spanning-tree mode mst End with CNTL/Z. © 2014 Cisco and/or its affiliates. we will ignore ALS1 and ALS2 for now. Page 3 of 12 .999 mode trunk nonegotiate Step 3: Configure VTP and VLANs To simplify the lab configuration.CCNPv7 SWITCH: Lab 4-2 – Multiple Spanning Tree Setting device to VTP Server mode DLS1(config)# int ran f0/7-12 DLS1(config-if-range)# switchport DLS1(config-if-range)# switchport DLS1(config-if-range)# switchport DLS1(config-if-range)# switchport DLS1(config-if-range)# switchport DLS1(config-if-range)# no shut DLS1(config-if-range)# exit DLS1(config)# for VLANS. DLS1(config)# Verify that all of the VLANs propogate and that there is a single root bridge for all of the VLANs. DLS1(config)# vtp domain SWLAB Changing VTP domain name from NULL to SWLAB DLS1(config)# vtp version 2 DLS1(config)# vlan 99 DLS1(config-vlan)# name MANAGEMENT DLS1(config-vlan)# vlan 100 DLS1(config-vlan)# name SERVERS DLS1(config-vlan)# vlan 110 DLS1(config-vlan)# name GUEST DLS1(config-vlan)# vlan 120 DLS1(config-vlan)# name OFFICE DLS1(config-vlan)# vlan 999 DLS1(config-vlan)# name PARKING_LOT DLS1(config-vlan)# state suspend DLS1(config-vlan)# vlan 666 DLS1(config-vlan)# name NATIVE_DO_NOT_USE DLS1(config-vlan)# exit *Mar 1 00:18:41. DLS1# conf t Enter configuration commands. This document is Cisco Public. one per line. This configuration will propagate to the other switches in the network. Step 4: Implement Multiple Spanning Tree In this step you will implement MST on DLS1 and DLS2. configure VTP version 2 on DLS1 with no password. one per line. All rights reserved. and configure VLANs for use in the network. trunk encap dot1q trunk native vlan 666 trunk allowed vlan except 1.

All rights reserved. number 1. Step 6: Manually Configure MST Now configure MST on both DLS1 and DLS2 with the following information (you must configure each switch manually):  Region Name: CCNP  Revision Number: 1  VLAN Mappings: Instance 1: VLAN 99 and VLAN 100 MST region configuration is performed in a special mode under the global configuration that is entered using the spanning-tree mst configuration command. and VLANS 1-4094 are mapped to that instance For MST to work. MST is running with default parameters. you can use the show current and show pending commands to see how the configuration stands. it is just an administrator-assigned value). While in MST configuration mode. the region must be named and given a revision number (this revision number does not work like VTP. issue the command show spanning-tree mst configuration to see the configuration information: DLS1# show span mst configuration Name [] Revision 0 Instances configured 1 Instance Vlans mapped -------. Page 4 of 12 . and have the same VLAN-to-instance mapping. You have to make the changes and exit from configuration mode to have the changes applied.--------------------------------------------------------------------0 1-4094 ------------------------------------------------------------------------------DLS1# The output tells us The region is un-named  The revision number is 0  There is one instance of MST. From DLS1: © 2014 Cisco and/or its affiliates.CCNPv7 SWITCH: Lab 4-2 – Multiple Spanning Tree DLS1(config)#exit DLS1# clear spanning-tree detected-protocols DLS1# DLS1# show spanning-tree MST0 Spanning tree enabled protocol mstp Root ID Priority 32768 Step 5: Observe default MST configuration At this point. On DLS1. the changes are not applied until you exit. All the switches in the same region must have the same region name and revision number. This document is Cisco Public.

one per line.101-4094 1 99-100 ------------------------------------------------------------------------------DLS1(config-mst)# DLS1(config-mst)#exit DLS1(config)#end DLS1# DLS1# show span mst config Name [CCNP] Revision 1 Instances configured 2 Instance Vlans mapped -------. DLS1(config)# spanning-tree mst configuration DLS1(config-mst)# name CCNP DLS1(config-mst)# revision 1 DLS1(config-mst)# instance 1 vlan 99.100 DLS1(config-mst)# DLS1(config-mst)# show current Current MST configuration Name [] Revision 0 Instances configured 1 Instance Vlans mapped -------. End with CNTL/Z.101-4094 1 99-100 ------------------------------------------------------------------------------DLS1# Wait a moment to let the topology settle and then issue the show spanning-tree mst command on DLS1: DLS1# show spanning-tree mst © 2014 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public.--------------------------------------------------------------------0 1-98.CCNPv7 SWITCH: Lab 4-2 – Multiple Spanning Tree DLS1# conf t Enter configuration commands.--------------------------------------------------------------------0 1-98. Page 5 of 12 .--------------------------------------------------------------------0 1-4094 ------------------------------------------------------------------------------DLS1(config-mst)# DLS1(config-mst)# show pending Pending MST configuration Name [CCNP] Revision 1 Instances configured 2 Instance Vlans mapped -------.

406f.13 128. ALS1 and ALS2 are running the default PVST.406f. which simplifies this process considerably. configuration revision.10 128.Nbr -------128.14 0) 0) 32769 (32768 sysid 1) 32769 (32768 sysid 1) 200000 rem hops 19 Type -------------------------------P2p Bound(PVST) P2p Bound(PVST) P2p Bound(PVST) P2p Bound(PVST) P2p P2p As you can see from the output above. All rights reserved.101-4094 address e840.12 128. This document is Cisco Public.7280 priority 32768 (32768 sysid address e840.CCNPv7 SWITCH: Lab 4-2 – Multiple Spanning Tree ##### MST0 Bridge Root vlans mapped: 1-98. Step 7: Propagate MST configurations with VTP Manual configuration of MST is not particularly difficult until the network scales to a large size. While having multiple regions is not an error per se.406f.13 128.406f.7280 address e840. in this case.6e00 port Fa0/11 Interface ---------------Fa0/7 Fa0/8 Fa0/9 Fa0/10 Fa0/11 Fa0/12 Role ---Desg Desg Desg Desg Root Altn Sts --FWD FWD FWD FWD FWD BLK Cost --------200000 200000 200000 200000 200000 200000 0) 19 6 20 Type -------------------------------P2p Bound(PVST) P2p Bound(PVST) P2p Bound(PVST) P2p Bound(PVST) P2p P2p priority priority cost Prio. For switches to form a single MST region. Page 6 of 12 . This is the entry shown when the device connected at the other end of the given interface is not running MST. each region having its own internal root bridges for the defined MST instances and independent internal topologies. max age 20.9 128.10 128. max age 20. the VLANs are mapped to the correct instance and the root bridge for both instances is not the local switch (it is DLS2 in this case).11 128. and some large networks are even partitioned into multiple regions intentionally. © 2014 Cisco and/or its affiliates.9 128. max hops Interface ---------------Fa0/7 Fa0/8 Fa0/9 Fa0/10 Fa0/11 Fa0/12 ##### MST1 Bridge Root Role ---Desg Desg Desg Desg Root Altn Sts --FWD FWD FWD FWD FWD BLK Cost --------200000 200000 200000 200000 200000 200000 Prio. they must match in all region parameters: region name.406f. running multiple MST regions as a result of region misconfiguration is undesirable.Nbr -------128. VTP version 3 allows for the sharing of the MST database amongst switches. forward delay 15. Switches that differ in their MST region configuration will form separate regions. txholdcount Configured hello time 2 .6e00 priority 32768 (32768 sysid internal cost 200000 rem hops Operational hello time 2 . Notice the type entry P2p Bound(PVST).11 128.12 128.6e00 priority 32768 (32768 sysid port Fa0/11 path cost 0 Regional Root address e840. VLAN-to-instance mappings.14 vlans mapped: 99-100 address e840. forward delay 15.

DLS2(config)# end DLS2# vtp primary mst This system is becoming primary server for feature mst No conflicting VTP3 devices found. Version 3 files will be written in the future. Step 8: Verify Initial MST Configuration After the entire configuration is done. Do not forget to activate MST on all switches. VTP version 3 will propagate the MST configuration to the other switches.386: %SW_VLAN-6-OLD_CONFIG_FILE_READ: Old version 2 VLAN configuration file detected and read OK. Note: An identical MST region configuration will be propagated to all switches within a VTPv3 domain. Page 7 of 12 . All rights reserved. ALS1(config)# end End with CNTL/Z.217: %SW_VLAN-4-VTP_PRIMARY_SERVER_CHG: e840. DLS2(config)# vtp version 3 DLS2(config)# *Mar 1 00:49:27. This document is Cisco Public.406f. one per line. From DLS2: DLS2# conf t Enter configuration commands. ALS1(config)# spanning-tree mode mst ALS1(config)# vtp version 3 ALS1(config)# vtp mode server mst Setting device to VTP Server mode for MST. End with CNTL/Z. Do you want to continue? [confirm] DLS2# *Mar 1 00:55:45. VTP version 3 will synchronize only the region configuration across all switches and will not affect the STP version running on the switch. DLS2(config)# DLS2(config)# vtp mode server mst Setting device to VTP Server mode for MST.CCNPv7 SWITCH: Lab 4-2 – Multiple Spanning Tree To use VTP version 3 to propagate the MST region configuration to all switches in the VTP domain. there is always a one-to-one mapping between a VTPv3 domain and an MST region. Then designate one switch as the VTP primary for MST. As a result. Verify this by checking ALS2: ALS2# show spanning-tree mst configuration Name [CCNP] Revision 1 Instances configured 2 Instance Vlans mapped © 2014 Cisco and/or its affiliates. convert all switches to VTP version 3 and set them as servers or clients for MST. and consequently they will all form a single region.7380 has become the primary server for the MST VTP feature From ALS1 (the same configuration must be applied at ALS2): ALS1# conf t Enter configuration commands. one per line.

120 DLS2(config-mst)# show pending Pending MST configuration Name [CCNP] Revision 1 Instances configured 3 End with CNTL/Z. one per line.10 128.CCNPv7 SWITCH: Lab 4-2 – Multiple Spanning Tree -------. max hops 20 Interface ---------------Fa0/7 Fa0/8 Fa0/9 Fa0/10 Fa0/11 Fa0/12 ##### MST1 Bridge Root Role ---Desg Desg Desg Desg Desg Desg Sts --FWD FWD FWD FWD FWD FWD Cost --------200000 200000 200000 200000 200000 200000 Prio. txholdcount 6 hello time 2 . forward delay 15.1680 this switch for MST1 Interface ---------------Fa0/7 Fa0/8 Fa0/9 Fa0/10 Fa0/11 Fa0/12 Role ---Desg Desg Desg Desg Desg Desg Sts --FWD FWD FWD FWD FWD FWD Cost --------200000 200000 200000 200000 200000 200000 Type -------------------------------P2p P2p P2p P2p P2p P2p priority Prio. mapping VLANs 110 and 120 to it. DLS2(config)# spanning-tree mst config DLS2(config-mst)# instance 2 vlan 110. add another instance on DLS2.1680 priority 32768 (32768 sysid 0) this switch for the CIST hello time 2 .11 128. forward delay 15.95cf. © 2014 Cisco and/or its affiliates.Nbr -------128.--------------------------------------------------------------------0 1-98.101-4094 1 99-100 ------------------------------------------------------------------------------ALS2#show span mst ##### MST0 Bridge Root Operational Configured vlans mapped: 1-98.101-4094 address 0017. max age 20.12 vlans mapped: 99-100 address 0017.10 128.11 128. max age 20.95cf.12 32769 (32768 sysid 1) Type -------------------------------P2p P2p P2p P2p P2p P2p Step 9: Modify MST Configuration To further illustrate the convenience of MST and VTP version 3.8 128. This document is Cisco Public.8 128. Page 8 of 12 .Nbr -------128. All rights reserved. DLS2# conf t Enter configuration commands.9 128.7 128.7 128.9 128.

101-109. txholdcount Configured hello time 2 .95cf.7280 priority 32768 (32768 sysid address 0017.95cf.7280 address 0017.111-119.--------------------------------------------------------------------0 1-98.101-109. forward delay 15.111-119.121-4094 1 99-100 2 110. forward delay 15.Nbr -------128.--------------------------------------------------------------------0 1-98.95cf.111-119.CCNPv7 SWITCH: Lab 4-2 – Multiple Spanning Tree Instance Vlans mapped -------.120 ------------------------------------------------------------------------------DLS1# show span mst ##### MST0 Bridge Root vlans mapped: 1-98.121-4094 1 99-100 2 110. max hops Interface ---------------Fa0/7 Fa0/8 Fa0/9 Fa0/10 Fa0/11 Fa0/12 ##### MST1 Bridge Root Role ---Altn Altn Root Altn Altn Altn Sts --BLK BLK FWD BLK BLK BLK Cost --------200000 200000 200000 200000 200000 200000 Prio.12 128.13 128.10 128.11 128.1680 priority 32768 (32768 sysid internal cost 200000 rem hops Operational hello time 2 . 32769 (32768 sysid 1) 32769 (32768 sysid 1) 200000 rem hops 19 Page 9 of 12 .406f.1680 priority 32768 (32768 sysid port Fa0/9 path cost 0 Regional Root address 0017. max age 20. max age 20.406f.1680 port Fa0/9 0) 0) 0) 19 6 20 Type -------------------------------P2p P2p P2p P2p P2p P2p priority priority cost © 2014 Cisco and/or its affiliates. All rights reserved.120 ------------------------------------------------------------------------------DLS2(config-mst)# DLS2(config-mst)# exit DLS2(config)# end DLS2# And then verify on that the changes propagated to another switch: DLS1# show span mst config Name [CCNP] Revision 1 Instances configured 3 Instance Vlans mapped -------.14 vlans mapped: 99-100 address e840. This document is Cisco Public.121-4094 address e840.9 128.101-109.

----.9 128.000 • 1 Gigabit Ethernet—20. All rights reserved.11 128. are different in MST: • 10 Mbps—2.7280 priority address 0017.13 128.1680 priority port Fa0/9 cost Interface ---------------Fa0/7 Fa0/8 Fa0/9 Fa0/10 Fa0/11 Fa0/12 Role ---Altn Altn Root Altn Altn Altn Sts --BLK BLK FWD BLK BLK BLK Cost --------200000 200000 200000 200000 200000 200000 Prio.--.120 address e840. which are the same as PVST with one exception – port cost values.9 128. Page 10 of 12 .11 128.14 32770 (32768 sysid 2) 32770 (32768 sysid 2) 200000 rem hops 19 Type -------------------------------P2p P2p P2p P2p P2p P2p Step 10: Manipulate the spanning tree To this point we have left election of the root bridge up to the protocol defaults.1680 200000 2 20 15 32770 0017.406f.Nbr -------128.000 • 10 Gigabit Ethernet—2.1680 200000 2 20 15 Root Port -----------Fa0/9 Fa0/9 Fa0/9 Port costs.Nbr -------128.--------.14 Type -------------------------------P2p P2p P2p P2p P2p P2p vlans mapped: 110.10 128.10 128.000 © 2014 Cisco and/or its affiliates.CCNPv7 SWITCH: Lab 4-2 – Multiple Spanning Tree Interface ---------------Fa0/7 Fa0/8 Fa0/9 Fa0/10 Fa0/11 Fa0/12 ##### MST2 Bridge Root Role ---Altn Altn Root Altn Altn Altn Sts --BLK BLK FWD BLK BLK BLK Cost --------200000 200000 200000 200000 200000 200000 Prio.95cf. An example of the show spanning-tree root command at DLS1 provides proof that the root bridge is elsewhere: DLS1# show spanning-tree root MST Instance ---------------MST0 MST1 MST2 DLS1# Root Hello Max Fwd Root ID Cost Time Age Dly -------------------. This document is Cisco Public. use much larger numbers.13 128. still based on the physical interface’s bandwidth.000. which are summed to find a path cost in the quest for a root bridge.12 128.95cf.95cf.1680 0 2 20 15 32769 0017.95cf.12 128.000 • 100 Mbps—200.--32768 0017.

use the command spanning-tree mst instance-list root {primary | secondary} global configuration command. we will shutdown interfaces Fa0/9-10 on DLS2 and then change the port cost value of ALS2’s interface Fa0/7 to a lower number. DLS2(config)# spanning-tree mst 0-1 root secondary DLS2(config)# spanning-tree mst 2 root primary DLS2(config)# end DLS2# The results of these configuration changes are evident using the show spanning-tree root command. From ALS1. Path cost is the sum of Port Costs. To manually configure a bridge to be the primary MST root.CCNPv7 SWITCH: Lab 4-2 – Multiple Spanning Tree MST uses the same basic commands and values to manipulate it’s operation. root primary for instance 2 and root secondary for instances 0 and 1: DLS2# conf t Enter configuration commands.406f. one per line. one per line.----. End with CNTL/Z.--0 2 20 15 200000 2 20 15 200000 2 20 15 Root Port -----------Fa0/7 Fa0/7 Fa0/9 As with PVST. and the secondary root for instance 2: DLS1# conf t Enter configuration commands. causing the spanning tree for instance 2 to go through ALS2.6e00 Root Hello Max Fwd Cost Time Age Dly --------. Page 11 of 12 . Root Port selection is based on total path cost to the root bridge.--. You can also manually set the bridge priority using the spanning-tree mst instance-list priority priority global configuration command. You can configure the port costs using the spanning-tree mst instance cost value interface configuration command.406f.406f. which sets the cost for that instance alone. End with CNTL/Z. DLS1(config)# spanning-tree mst 0-1 root primary DLS1(config)# spanning-tree mst 2 root secondary DLS1(config)# end DLS1# DSL2 is configured with a complementary set of instructions. All rights reserved. which shows Fa0/7 (connected to DLS1) as the Root Port for instances 0 and 1 and Fa0/9 (connected to DLS2) for instance 2: ALS1# show spanning-tree root MST Instance ---------------MST0 MST1 MST2 ALS1# Root ID -------------------24576 e840.7280 24577 e840. This document is Cisco Public. © 2014 Cisco and/or its affiliates. DLS1 is configured as the primary root for instance 0 and 1. In the example below. As an implementation example.7280 24578 e840.

406f.CCNPv7 SWITCH: Lab 4-2 – Multiple Spanning Tree On ALS2: ALS2# config t ALS2(config)# int f0/7 ALS2(config-if)# spanning-tree mst 2 cost 1000 ALS2(config-if)# exit ALS2(config)# end On DLS2: DLS2# conf t Enter configuration commands.tcl” created in Lab 1 to clear and reload all of your switches before the next lab. And then finally examining ALS1: ALS1# show spanning-tree root MST Instance ---------------MST0 MST1 MST2 ALS1# Root ID -------------------24576 e840. This document is Cisco Public. All rights reserved.7280 24578 e840.----. Page 12 of 12 .--0 2 20 15 200000 2 20 15 201000 2 20 15 Root Port -----------Fa0/7 Fa0/7 Fa0/11 Step 11: End of Lab Use the tcl script “reset. DLS2(config)# interface ran f0/9-10 DLS2(config-if-range)# shut DLS2(config-if-range)# end End with CNTL/Z.6e00 Root Hello Max Fwd Cost Time Age Dly --------. © 2014 Cisco and/or its affiliates.406f.--.406f.7280 24577 e840. one per line.