3750 stacking question

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Jul 1st, 2009
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We have a stack of 3 3750 which are provisioned


switch 1 provision ws-c3750g-48ts

switch 2 provision ws-c3750g-48ts

switch 3 provision ws-c3750g-12s


My question is that if we reboot these switches will they retain their member numbers or will they re calculate the value? I dont see any commands in the running config whih specifically gives any switch a manual priority or member number. How will the master be elected and will the provisioning assign the member ID's or is it just used for adding a switch to a stack?


thanks in advance

Correct Answer by will.cullen about 7 years 11 months ago

I'm not familar with the "show platform stack-manager all" command, but if you us the "show switch" command if the switches are at default ie straight out the box then the priority will be set to 1. If you see anything else then the priority has been changed, once the priority has been changed the switches should keep this change even after a reboot.

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xcz504d1114 Wed, 07/01/2009 - 10:36
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You can manually set the switch numbers and switch priority in global configuration from any switch in the stack.


conf t

switch 1 priority 10

switch 2 priority 8

switch 3 priority 6


switch 1 renumber 1

switch 2 renumber 2

switch 3 renumber 3


The higher priority number becomes the master, manually specifying the renumber ensure it comes up as the correct switch number.


Here is a link that describes in great detail how stack members work.


http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_44_se/configuration/guide/swstack.html


HTH,

Craig

flyinhorse Wed, 07/01/2009 - 10:41
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thanks Craig.


So the provision is only used for adding switches to the stack and on reboot the switches will not retain their existing number and this has to be done manually? rite.

xcz504d1114 Wed, 07/01/2009 - 11:54
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Without manually configuring the switch stack priorities and numbers you cannot guarantee which switch will be the master, and what number order they will be placed in.


It is however reasonable to assume that if you powered all three switches on at the same time of configuration, configured them, then powered them all down and brought them back online the exact same way you took them down (assuming no changes in IOS) then they SHOULD come back online as you provisioned them.


Manual configuration of priority and numbers takes all of those questions away.



Here is a snippit taken from the link i provided.


The stack master is elected or re-elected based on one of these factors and in the order listed:


1. The switch that is currently the stack master.


2. The switch with the highest stack member priority value.


Note We recommend assigning the highest priority value to the switch that you prefer to be the stack master. This ensures that the switch is re-elected as stack master if a re-election occurs.


3. The switch that is not using the default interface-level configuration.


4. The switch with the higher priority switch software version. These switch software versions are listed from highest to lowest priority:


-Cryptographic IP services image software


-Noncryptographic IP services image software


-Cryptographic IP base image software


-Noncryptographic IP base image software


The Catalyst 3750 IP services image cryptographic image has a higher priority than the Catalyst 3750 IP base image during the master switch election in a stack. However, when two or more switches in the stack use different software images, such as the IP base image for Cisco IOS Release 12.1(11)AX and the cryptographic IP services image for Cisco IOS Release 12.1(19)EA1 or later, the switch running the IP base image is selected as the stack master. This occurs because the switch running the cryptographic IP services image takes 10 seconds longer to start than does the switch running the IP base image. The switch running the IP services image is excluded from the master election process that lasts 10 seconds. To avoid this problem, upgrade the switch running the IP base image to a software release later than Cisco IOS Release 12.1(11)AX or manually start the master switch and wait at least 8 seconds before starting the new member switch.


5. The switch with the lowest MAC address.


A stack master retains its role unless one of these events occurs:


•The switch stack is reset.*


•The stack master is removed from the switch stack.


•The stack master is reset or powered off.


•The stack master has failed.


•The switch stack membership is increased by adding powered-on standalone switches or switch stacks.*


In the events marked by an asterisk (*), the current stack master might be re-elected based on the listed factors.


When you power on or reset an entire switch stack, some stack members might not participate in the stack master election. Stack members that are powered on within the same 20-second time frame participate in the stack master election and have a chance to become the stack master. Stack members that are powered on after the 20-second time frame do not participate in this initial election and only become stack members.


How I typically configure my switch stacks is by booting them all up, then manually, labeling them (physically on the box with a label), then configuring the switch numbers and priorities based on those labels, so I label the top switch as switch 1, when it boots up, it might be switch 2 in the stack, it might be switch 1, who knows, it depends on the lowest mac-address. I then renumber and assign that switch with the highest priority. after I do this to all switches, I then reboot them and verify the master is who I expected it to be and the switch numbers are as i expected.


After that I can configure the switches and deploy them.


HTH,

Craig

xcz504d1114 Wed, 07/01/2009 - 11:55
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Here is another snippit regarding switch numbers and changing them on provisioned switches:


•If you manually change the stack member number by using the switch current-stack-member-number renumber new-stack-member-number global configuration command, the new number goes into effect after that stack member resets (or after you use the reload slot stack-member-number privileged EXEC command) and only if that number is not already assigned to any other members in the stack. For more information, see the "Assigning a Stack Member Number" section. Another way to change the stack member number is by changing the SWITCH_NUMBER environment variable, as explained in the "Controlling Environment Variables" section.


If the number is being used by another member in the stack, the switch selects the lowest available number in the stack.


If you manually change the number of a stack member and no interface-level configuration is associated with that new member number, that stack member resets to its default configuration. For more information about stack member numbers and configurations, see the "Switch Stack Configuration Files" section.


You cannot use the switch current-stack-member-number renumber new-stack-member-number global configuration command on a provisioned switch. If you do, the command is rejected.



Craig

flyinhorse Wed, 07/01/2009 - 12:16
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Thanks that helps, just one last thing Craig.


If i manually set these parameters will they show up on a show run? how can you tell if the parameters have been set or they are using their default values.


thanks.

xcz504d1114 Wed, 07/01/2009 - 12:22
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I don't remember right off hand if it shows up in the running configuration or not.


You can use the "show switch 1" to view the priority of switch one.


Also I believe you can use the "show version" command to display switch numbers and associate them with the mac-address on the switch, you can then look at the sticker on the back of the switch that tells you the mac-address.


And one more way to view this information is to use the mode button on the front left side of the switch, there is an option there that will use the port LED's to indicate which switch is what number and which one is master.


HTH,

Craig

flyinhorse Wed, 07/01/2009 - 12:40
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so basically there is no way to know if some one has already configured these parameters manually or the switches are using the default setup since last time they were brought online?


If you run the commad


show platform stack-mamager all


there is a table with the field "Default Config". if this field says "NO" does it mean the config was manually chaged like member and priority numbers?

Correct Answer
will.cullen Wed, 07/01/2009 - 12:59
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I'm not familar with the "show platform stack-manager all" command, but if you us the "show switch" command if the switches are at default ie straight out the box then the priority will be set to 1. If you see anything else then the priority has been changed, once the priority has been changed the switches should keep this change even after a reboot.

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