Cisco – Addition of new switch to an existing stack

ciscostackingswitch

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.

Best Answer

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.

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