Troubleshooting Switch Stacks
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Table Of Contents
Preventing Traffic Disruptions
Problem: Switch Does Not Join the Stack
Resolving Switch Compatibility Issues
Fixing Incompatible Cisco IOS Versions and Switch-Stack Protocol Versions
Resolving Software License Compatibility Issues
Resolving Incompatible Configurations
Fixing SDM Template Configuration Incompatibilities (Catalyst 3750G-12S Switches)
Resolving StackWise Connection Problems
Fixing Problems with StackWise Interfaces and Cables
Joining a Stack: Typical Sequence States and Rules
Using the Configuration Manager
Reviewing How the Stack Master Is Elected and Port Numbers Are Assigned
Reviewing How the Stack Master is Rebooted or Disconnected
Understanding Switch Hardware Priority and Stack Manager Version
Problem: Stack Ring Is Not Operating at Full Bandwidth
Resolving Bandwidth Issues (Catalyst 3750 and Catalyst 3750-E Switches)
Using LEDs to Verify StackWise Link Connections
Problem: StackWise Port is Flapping
Resolving Version Mismatches and Copying Files
Upgrading Catalyst 3750 and Catalyst 3750-E Switch Stacks
Troubleshooting Switch Stacks
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Preventing Traffic Disruptions
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Preventing Traffic Disruptions
Before you connect a switch to or disconnect a switch from a stack, power it off. Connecting or disconnecting the StackWise cables when switches are powered on can cause switch reloads or temporary traffic loss in the active switches.
Problem: Switch Does Not Join the Stack
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Resolving Switch Compatibility Issues
If a switch does not join a stack, look for incompatibilities between the stack master and member switches in relation to the Cisco IOS version, the license levels, and the configuration settings on the switches.
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Fixing Incompatible Cisco IOS Versions and Switch-Stack Protocol Versions
A new switch might not join a stack when Cisco IOS versions or stack protocol versions differ. Review these points about Cisco IOS versions and stack protocol versions:
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The stack master reports the reason for any incompatibility.
The Cisco IOS software version running on a switch that you plan to add to a switch stack must either be the same as or compatible with on the master switch version. After you connect a new switch to a switch stack, enter the show version user EXEC command to see the version information, the switch types, and the active Cisco IOS version for each switch:
Stack# show versionSwitch Ports Model SW Version SW Image------ ----- ----- ---------- ----------* 1 30 WS-C3750E-24PD 12.2(46)SE C3750E-UNIVERSAL-M2 28 WS-C3750E-24PS 12.2(46)SE C3750E-UNIVERSAL-M3 54 WS-C3750E-48TD 12.2(46)SE C3750E-UNIVERSAL-M...output truncatedIf stack members are running incompatible Cisco IOS versions, software version incompatibilities called mismatches occur. If you have a switch that cannot join a switch stack, enter the show switch user EXEC command to see whether the state of the switch is in Version Mismatch (see Switch 3):
Stack# show switchH/W CurrentSwitch# Role Mac Address Priority Version State----------------------------------------------------------*1 Master 0018.ba60.de00 15 1 Ready2 Member 0018.ba60.ce00 14 1 Ready3 Member 0016.9d0c.7500 1 2 Version MismatchTo see which software version switch 3 is running, enter the remote 3 show version command.
If the stack master detects that the software on a new switch does not match, it upgrades (or downgrades) the new switch with the active image that is running on the switch stack by using the automatic upgrade (auto-upgrade) and the automatic advise (auto-advise) features.
Switches with the same major version number but a different minor version number are considered partially compatible. When you connect a partially compatible switch to a stack, the new switch might enter version-mismatch mode and not join the stack as a functional member. The current state in this case is also Version Mismatch, which you can see by entering the show switch user EXEC command:
Stack# show switchH/W CurrentSwitch# Role Mac Address Priority Version State----------------------------------------------------------*1 Master 0018.ba60.de00 15 1 Ready2 Member 0018.ba60.ce00 14 1 Ready3 Member 0016.9d0c.7500 1 2 Version MismatchSee the "Resolving Version Mismatches and Copying Files" section and the "Understanding Switch Hardware Priority and Stack Manager Version" section for more information.
Resolving Software License Compatibility Issues
Mismatched or incompatible software license levels might prevent a Catalyst 3750E switch from joining a stack. These license levels are also called sets, or feature sets:
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Each member switch must have a compatible feature license. Otherwise, you need to upgrade the license level and then reload the switch.
To review the installed license in a member switch, enter these commands. In this example, member switches have the same license level:
Stack-1# show license all switch 1License Store: Primary License StorageStoreIndex: 0 Feature: advipservicesLicense Type: PermanentLicense State: Active, In UseStack-1# show license all switch 2License Store: Primary License StorageStoreIndex: 0 Feature: advipservicesLicense Type: PermanentLicense State: Active, In UseA switch can have up to three installed licenses, but only one is active. Use the show version user EXEC command to see the active licenses. This example is part of the output message for one stack:
Stack-1# show versionSwitch 03---------License Level : advipservicesLicense Type : PermanentNext reboot licensing Level : advipservicesSwitch 04---------License Level : advipservicesLicense Type : PermanentNext reboot licensing Level : advipservicesReload the switch after you upgrade the license level. See the appropriate software configuration guide for more information on license administration.
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Resolving Incompatible Configurations
A switch previously used as a standalone or in a different stack might have different configuration settings. Return the switch to its default values before you connect it to a new stack.
When you add a switch to a stack, the stack master automatically changes the configuration of the new switch. The master switch revises the new member switch port numbers to conform to the current port numbering sequence in the stack. Any existing port-level configuration in the newly-added switch is automatically cleared or updated.
If you add a switch that was a member of one stack to a different stack, the switch port numbers might be inappropriate. For example, instead of the Ethernet ports being numbered with the default values of Fa1/0/1 or G1/0/1, the port numbering might start with Fa2/0/1 or G2/0/1. If the port numbers begin with G2/0/1, for example, enter the switch renumber global configuration command to return switch ports to the default numbering values as shown in this example:
Switch(config)# switch 2 renumber 1When you reboot the switch, all port-level configurations are removed, and port numbering begins with Fa1/0/1 or G1/0/1.
To prevent incompatible configurations, follow these steps on a previously configured switch that you plan to add to the stack:
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Fixing SDM Template Configuration Incompatibilities (Catalyst 3750G-12S Switches)
The master switch automatically corrects SDM template mismatches in Catalyst 3750 and 3750E switches when you connect one of them to a stack. A configuration mismatch might occur if the switch was a Catalyst 3750G-12S switch configured with a nondefault SDM template before you connect it to a stack.
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See the appropriate software configuration guide for additional information on SDM templates.
Resolving StackWise Connection Problems
These sections discuss how to resolve problems with StackWise connections:
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When you connect a switch to a stack, make sure you properly connect both StackWise cables. It is possible for a switch to join a stack when only one StackWise cable is connected to another active stack member, in which case the stack operates at less than maximum ring bandwidth.
An open ring operates at half the available bandwidth. After you connect both StackWise cables of the new switch and it has joined the ring, full ring bandwidth is restored.
Consider these precautions when you connect StackWise cables:
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When you troubleshoot suspected cable connection problems, use the show switch user EXEC command to review the status of switches in the stack. In this example, you can see that switch #3 is in the
Provisionedstate, which means you need to investigate why. See the descriptions in Table 1.
Fixing Problems with StackWise Interfaces and Cables
A defective StackWise interface might prevent a switch from joining a stack and can also cause stack port flapping. The best way to test a StackWise interface is by using a known good StackWise cable to connect the two StackWise interfaces. The switch should report a good connection when you enter the show switch detail user EXEC command.
StackWise cable connection problems are usually caused by a loose connection, not a defect in the cable or connector. If two StackWise cables are connected to another stack member, the switch should join the stack even if one of the cables is defective. If you connect only one StackWise cable to a switch and the connection is unreliable, that switch might not join the stack.
The best way to test a StackWise cable that you suspect is defective is to replace it with a known-good cable. If replacing the cable solves the problem, the replaced cable is possibly defective. However, an unreliable connection that was corrected when you replaced the cable might also have been the cause.
If you do not have replacement cable, use these steps to verify whether a cable or a stack member port is faulty:
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You can also test a StackWise cable or interface by using only one cable and one switch. Connect the StackWise cable to both StackWise interfaces on the same switch (see Figure 1).
Figure 1 Using One Cable and Switch to Test a StackWise Cable or Interface
Boot or reboot the switch. This message appears:
SM: Detected stack cables at PORT1 PORT2The message does not conclusively mean that there are no problems with the interfaces or cable. However, the cable and the member ports are probably good.
If a StackWise cable is connected to both StackWise ports on the switch and this message appears, either the cable is defective or StackWise port 2 is defective:
SM: Detected stack cables at PORT1Enter the show switch detail user EXEC command to review the status of specific StackWise interfaces:
The switches in this example are active stack members, but the ring is incomplete. This example is typical of a missing cable between two switches. After you connect a known-good cable between switch 1 and switch 3, the stack ports become active and show a status of OK. This situation might be a switch hardware problem, but before you replace a switch, verify that the StackWise cables are correctly connected; that is, make sure the retainer screws are equally tightened.
This shows the results of an added StackWise cable between switch 1, port 1 and switch 3, port 2. All StackWise ports are active, and the ring is complete. Full stack bandwidth is available.
The retainer screw shown on the top of the connection shown in Figure 2 is not fully engaged, which can result in the connector working itself loose. The best practice is to finger-tighten both retainer screws to the same degree.
Figure 2 Example of Loose Retainer Screw
Resolving Stack Partitions
An improperly connected ring, a member switch failure, or a faulty StackWise cable connection can cause a stack partition. The stack separates into two independent stacks, each with a stack master. A stack partition usually changes configuration and port numbering. Each stack might also have the same IP address assigned to a switch virtual interface (SVI), which results in a duplicate IP address.
Joining a Stack: Typical Sequence States and Rules
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This example shows a typical sequence when adding a switch to a stack:
This sequence takes several minutes. Continue to enter the show switch user EXEC command to see the current status.
These are other states that you might see when a switch is joining a stack:
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After an automatic Cisco IOS upgrade corrects a detected Cisco IOS feature mismatch, the upgraded switch reloads before becoming a fully operational stack member.
Using the Configuration Manager
The configuration manager is a Cisco IOS control program that runs on the stack master. The configuration manager performs these functions:
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Using the Stack Manager
The Stack Manager is a Cisco IOS program that runs on the stack master switch and performs these tasks:
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Reviewing How the Stack Master Is Elected and Port Numbers Are Assigned
All member switches participate in the election of a stack master if they all boot-up within the election window (20 to 60 seconds). The minimum time depends on which Cisco IOS version is running on the switches. This message appears:
Waiting for Master ElectionAny switches that you connect to the stack after the election process completes are considered stragglers and do not participate in the stack master election. These are the procedural rules for electing a stack master:
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Switch(config)# switch 5 renumber 1•
Member switches wait for the master to report a complete initialization, then this message appears:
Waiting for Master ReadyTo identify the stack master:
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An active switch connected to a fully operational stack becomes a stack member. It receives the running configuration from the stack master. When you disconnect a stack member, the switch numbers and port numbers of the remaining stack members do not change, and the switches do not reload.
Reviewing How the Stack Master is Rebooted or Disconnected
A new stack master is elected when you:
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These rules determine switch priority:
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Stack(config)# switch 1 priority 15You can then assign a lower priority to the remaining switches in the stack, or they can remain at default. A priority 15 switch overrides these selection decisions:
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Stack master and switch priority conflicts are resolved in this order:
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Understanding Switch Hardware Priority and Stack Manager Version
Stack hardware priority is a number associated with a specific switch model. Two different switch models can have the same hardware priority. Higher priority numbers increase the probability of a switch being elected the stack master.
The hardware priority is sent in Stack Manager messages and has a value between 15 and 0. (When you manually assign the priority, the range is 15 to 1.) For example, a Catalyst 3750-E switch typically has a default hardware priority of 5. The Catalyst 3750 switches typically have a default hardware priority of 2.
Switch hardware priority is different from the switch hardware version. The hardware version number is associated with the switch model. Different switch models can have same hardware version if they support the same system level features. (A higher version number does not always mean more capability.) This number is not used in stack master election.
This example shows the hardware priority and the hardware version:
Stack2# show switchH/W CurrentSwitch# Role Mac Address Priority Version State----------------------------------------------------------*1 Master 0018.ba60.de00 15 1 ReadyThe stack manager version is also called the image version and has major and minor version numbers as shown in this example:
Main problems related to minor version number mismatches:
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To resolve these problems, install the correct Cisco IOS version in the switch with the mismatch.
In some cases, the minor version is different in member switches, which might result in a version mismatch. With a new Cisco IOS version, the minor version might increase.
This example shows the Cisco IOS version running on each switch in a stack:
Stack# show versionSwitch Ports Model SW Version SW Image------ ----- ----- ---------- ----------* 1 30 WS-C3750E-24PD 12.2(46)SE C3750E-UNIVERSAL-M2 30 WS-C3750E-24PD 12.2(46)SE C3750E-UNIVERSAL-MSee the "Resolving Switch Compatibility Issues" section and the "Resolving Version Mismatches and Copying Files" section for more information.
Problem: Stack Ring Is Not Operating at Full Bandwidth
To operate at full bandwidth, a stack requires a closed ring. If only one StackWise cable is connected to the first and last switches in the stack, or if the ring is incomplete, less than full bandwidth is achieved.
These issues can cause an incomplete ring, in order of probability from high to low:
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These issues might cause a bad connection with an otherwise good cable:
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See the "Fixing Problems with StackWise Interfaces and Cables" section and the "Resolving StackWise Connection Problems" section for more information.
See these sections:
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Resolving Bandwidth Issues (Catalyst 3750 and Catalyst 3750-E Switches)
To troubleshoot problems associated with a stack ring not operating at full bandwidth, you need to know what bandwidth you can expect.
This is the maximum theoretical ring speed (bandwidth) for a Catalyst 3750 switch:
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This is the maximum theoretical ring speed (bandwidth) for a Catalyst 3750-E switch:
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To display the active Cisco IOS versions and switch models in a stack, enter the show version user EXEC command:
Stack# show versionSwitch Ports Model SW Version SW Image------ ----- ----- ---------- ----------* 1 30 WS-C3750E-24PD 12.2(46)SE C3750E-UNIVERSALK9-M2 28 WS-C3750G-24PS 12.2(46)SE C3750-IPSERVICESK9-M3 54 WS-C3750E-48TD 12.2(46)SE C3750E-UNIVERSALK9-M...output truncatedTo display information related to the stack member or the switch stack, enter the show switch user EXEC command:
Stack# show switchSwitch/Stack Mac Address : 0018.ba60.de00H/W CurrentSwitch# Role Mac Address Priority Version State----------------------------------------------------------*1 Master 0018.ba60.de00 15 1 Ready2 Member 0016.47f4.e300 14 0 Ready3 Member 0018.ba60.c700 13 1 ReadyThis example shows a mixed stack of Catalyst 3750-E and 3750G switches. All switches have joined the stack, but not all are running the same Cisco IOS version. All switches in a stack should be running the same Cisco IOS version (or equivalent Cisco IOS version in the case of mixed Catalyst 3750-E and 3750 switch stacks).
Enter the show switch stack-ring speed user EXEC command to see the StackWise bandwidth:
Use the show switch detail user EXEC command to see the status of all StackWise interfaces in the stack. The switches in this example are all active stack members, but the ring is incomplete:
A StackWise cable has been added between switch 1, port 1 and switch 3, port 2. All StackWise ports are connected and active, and the ring is complete. Full stack bandwidth is available. This is an excerpt of the output from the show switch detail user EXEC command:
Using LEDs to Verify StackWise Link Connections
You can test StackWise ring bandwidth by using the switch front-panel LEDs:
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Problem: StackWise Port is Flapping
These conditions might cause StackWise port flapping:
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When one or more StackWise ports are flapping, the source of the problem is probably an unreliable connection between a StackWise cable and a StackWise switch port.
If you suspect StackWise port flapping, first verify that the retainer screws are adequately tightened and fully seated against the connector shell. Make sure both retainer screws are tightened the same amount. In some cases you need to disconnect and reconnect the cable while you are troubleshooting, but do not test the connection unless the retainer screws are firmly holding the connector.
An unreliable StackWise connection might produce a similar error message:
#STACKMGR-4-STACK_LINK_CHANGE: Stack Port 1 Switch 1 has changed to state UPSTACKMGR-4-STACK_LINK_CHANGE: Stack Port 1 Switch 1 has changed to state DOWNSTACKMGR-4-STACK_LINK_CHANGE: Stack Port 1 Switch 1 has changed to state UPSTACKMGR-4-STACK_LINK_CHANGE: Stack Port 1 Switch 1 has changed to state DOWNSTACKMGR-4-STACK_LINK_CHANGE: Stack Port 1 Switch 1 has changed to state UPSTACKMGR-4-STACK_LINK_CHANGE: Stack Port 1 Switch 1 has changed to state DOWN-- or --
#STACKMGR-4-STACK_LINK_CHANGE: Stack Port 1 Switch 4 has changed to state UPSTACKMGR-4-STACK_LINK_CHANGE: Stack Port 2 Switch 5 has changed to state UPSTACKMGR-4-STACK_LINK_CHANGE: Stack Port 1 Switch 4 has changed to state DOWNSTACKMGR-4-STACK_LINK_CHANGE: Stack Port 2 Switch 5 has changed to state DOWNSTACKMGR-4-STACK_LINK_CHANGE: Stack Port 1 Switch 4 has changed to state UPSTACKMGR-4-STACK_LINK_CHANGE: Stack Port 1 Switch 4 has changed to state DOWNSUPQ-4-CPUHB_RECV_STARVE: Still seeing receive queue stuck after throttlingSTACKMGR-4-STACK_LINK_CHANGE: Stack Port 2 Switch 5 has changed to state UPSTACKMGR-4-STACK_LINK_CHANGE: Stack Port 2 Switch 5 has changed to state DOWNAn unreliable cable connection caused both of these patterns. Neither the StackWise cable nor the StackWise port was defective. A bad connection between the StackWise cable and the stack connector on the switch caused the problem.
A problem at either end of a StackWise link might cause port flapping at the other end of the link.
See the "Fixing Problems with StackWise Interfaces and Cables" section and "Resolving StackWise Connection Problems" section.
Resolving Version Mismatches and Copying Files
The remote file system runs on the stack master. You can use it to:
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Review these points about stack administration and Cisco IOS upgrades:
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When version mismatches occur on a member switch, you can review the contents of flash memory in the mismatched switch. This command shows the contents of flash memory for switch 3 in the stack:
Switch# dir flash3:If you previously upgraded the switch with the archive download-sw privileged EXEC command, the Cisco IOS file is in a subdirectory in flash memory. You can display the contents by using this command:
Switch# dir flash3:/c3750e-universal-mz.122-25.SEAn automatic upgrade can occur in most cases when a Cisco IOS version that is running on the stack master is not the same as the Cisco IOS version on the switch in mismatched mode. The automatic upgrade requires the Cisco IOS tar file of the current image to be available to any of the stack members. The tar file is stored in the flash memory on one of the switches in the stack, preferably the stack master.
If the tar file of the current image is not available, we recommend that you download a compatible image by using the appropriate commands and TFTP.
The automatic upgrade and auto-advise features do not work if the stack master and the switch in mismatched mode run different feature sets (IP Services and IP Base, for example). Starting with Cisco IOS Release 12.2(35)SE, automatic upgrade supports upgrades between cryptographic and noncryptographic images of the same feature set.
If automatic upgrade is not functional, you can manually copy a Cisco IOS file from one switch to another by using this command:
Stack# copy flash1:c3750e-universal-mz.122-35.SE1.bin flash3:This example copies the Cisco IOS file from flash memory in switch 1 to the flash memory in switch 3. If the bin file is in a subdirectory, this is the appropriate command:
Stack# copy flash1:/c3750e-universal-mz.122-35.SE1/c3750e-universal-mz.122-35.SE1.bin flash3:After you copy the new Cisco IOS file to the switch that is in version mismatch mode, you can delete the mismatched Cisco IOS file. Use this command to delete the unneeded subdirectory from switch 3 flash memory:
Stack# remote command 3 delete /recursive /force flash:/c3750e-universal-mz.122-25.SENext, reboot the upgraded switch to load and run the compatible Cisco IOS version:
Stack# reload slot 3After the switch reloads and loads the compatible Cisco IOS version, it joins the stack.
Upgrading Catalyst 3750 and Catalyst 3750-E Switch Stacks
This section includes some useful options for upgrading switch stacks. See the software configuration guide for routine software upgrade procedures for switches in a stack.
When both a Catalyst 3750-E switch and a Catalyst 3750 switch are in the same mixed stack, you can simultaneously upgrade both by using this command syntax:
stack# archive download-sw tftp://server/3750E.tar tftp://server/3750.tarThis might be a typical command string:
stack# archive download-sw tftp://192.168.1.1/3750E.tar tftp://192.168.1.1/3750.tarYou might have to specify the TFTP path if you do not copy the Cisco IOS file from the default TFTP directory on the TFTP server:
stack# archive download-sw tftp://server/path/3750E.tar tftp://server/path/3750.tarIf you do not need the HTML files, you can use the command option archive download-sw /image to install only the bin file to the flash memory in the Cisco IOS directory of each stack member. By eliminating the HTML files, the Catalyst 3750 switch uses less flash memory, and installation time is faster. Cases might occur where insufficient space is available in the flash memory to extract and install a complete tar file, Use the command option archive download-sw /image to save flash memory by installing only the IOS bin file in flash memory:
stack# archive download-sw /image tftp:// ...This command might be useful when you upgrade from older Cisco IOS versions in a mixed stack:
stack# archive download-sw /allow-feature-upgrade tftp:// . . .This is a typical combination:
stack# archive download-sw /image /allow tftp:// . . .You can also copy a Cisco IOS bin file to any specific switch in the stack, and then reload that switch. This example shows upgrading switch #2 in the stack:
Switch-1# copy tftp flash2:Address or name of remote host [ ]? ip addressSource filename [ ]? /path/filenameSwitch# config tSwitch(config)# boot system switch 2 filenameSwitch(config)# endswitch# reload slot 2Proceed with reload? [confirm]If the bin file is in a directory path in flash memory, use this command:
Switch(config)# boot system switch 2 directory/filename.binAlways use the archive download-sw command to upgrade Cisco IOS in any switch because using that command automatically sets the correct boot variable. As an alternative when necessary, you can copy a Cisco IOS bin file to any specific switch in the stack and then reload that switch.
When you copy a bin file to flash memory, the boot variable is not set. Upgrading a switch by using the archive download-sw /image command sets the correct filename in the boot variable.
See the appropriate switch software configuration guide for more information about stack upgrades.
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