I have a existing switch stack with 5 switches in the stack (all of them are 3750). Now, I have to add another switch (3750) to that stack. I turned on the new switch that I got from my company to make sure if there is any unnecessary configurations, and I found out that the the member number of the new switch is 1 (which is default) and the priority is set as 15.

Here is how I am planing to add this switch:

  1. Turn off the power of the new switch
  2. connect the stacking cable (according to Cisco documentation)
  3. Turn on the power of the new switch

By doing this the switch should automatically get the stack number and priority value of 1.

Now my question is: since the new switch has priority value of 15 before adding it to the stack, after adding the switch to the stack following above procedure, can this switch reboot the entire stack and reelect the master switch? If yes, how can I avoid this.

2 Answers 2


You should set the switch number and priority before adding it to the stack. You should also define the new switch on the stack before adding it to the stack, and you should verify that it is running the same IOS version as the stack before adding it to the stack. A switch will not automatically change its priority when added to the stack.

On the stack you should have the switch priority set on each the way you want. Don't depend on an election of equal priority members. The best practice is to manually set the switch priorities so that you have a deterministic failover. For instance:

Existing stack:

Switch 1: priority 15 (master)
Switch 2: priority 14
Switch 3: priority 13
Switch 4: priority 12

New switch:

Switch 5: priority 11

There is always a risk when adding something to a device or stack that the device or stack will reboot, but adding an unpowered switch to the stack, then powering it up, should not cause the stack to reboot.

  • Hi Ron, Thanks for your answer. This will be by approach for this job. Please verify this. New Switch: Before adding to the stack check the IOS version of the new switch and stack. If they match then use the following command. #switch 1 priority 1 #switch 1 renumber 7 #reload Switch Stack: Before adding the new switch #switch 7 provision ws-c-3750-48 1.Power of the new switch and add the switch to the stack using stack cables. 2.Turn on the power of the new switch. 3.Verify the stack using command #show switch detail
    – user25763
    Jul 5, 2016 at 20:46
  • That should work. Also, when creating a new stack, it is better to set each switch individually before connecting as a stack. It get ugly when trying to straighten it out after you have connected the stack.
    – Ron Maupin
    Jul 5, 2016 at 20:48

OK Guys, After looking into the answers and help by Ron, this is how i completed the project. I console into the new switch that was being added to stack and check the IOS image installed in the switch. Then i checked the IOS image installed in the stack. As the images were different I had to download IOS that matched the stack. I went to cisco.com to get the IOS. For this you will need the credential to login and from there you can browse to pick the desired IOS. After downloading the IOS, i saved it in the TFTP server folder. Then I consoled back into my new switch and formated the flash of the new switch [using command sw#format flash: ] since there was not enough space to save the new IOS. After that, I transferred the IOS from the tftp folder to flash of the new switch using the TFTP server. Once the IOS was in the flash, I went to config mode of the switch and used the command:

sw(config)# boot system flash:/c3750-ipbasek9-mz.122-55.SE6.bin

sw(congig)# do reload

This rebooted my switch with the new IOS and there was the IOS that matched my IOS with the stack in the new switch. I did this on both of my new switches.

After that, while i was consoled into my new switch before adding them to the stack, I change their priority to 1. I didnt renumber them.

Then, I went to my stack before adding the new switch and used the command:

stack(config)#switch 7 provision ws-c3750-48p

stack(config)# do wr

I had my new switches turned off before adding to stack. I installed the switch connected the stack cables to the new switch and stack and tunred on the power. The switch powered on and after a couple of second it became the member of the stack. and there you go all done.

Anyways I want to thank Ron for his help on this.

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