STACKWISE 3850 SWITCHES

[gerdlucyvend22]

I currently have 2 3850 Switches on my network. Both have configuration, that is, interfaces, vlans, SVIs. My question is, when forming stackwise, is the configuration of both maintained? Or is only the master configuration maintained and the standby configuration reset?

[Kasun Bandara]

@gerdlucyvend22 hi, master device's base config will replace the standby switch's config. i suggest you to clean the configs first and build the stack. then do configurations after stack built.

[Joseph W. Doherty]

There's just a single config for whole stack which all stack members have a copy of.

[balaji.bandi]

adding to other post - is the Physical Stacking, or Stackwise (look stackwise documentation)

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/16-9/configuration_guide/stck_mgr_ha/b_169_stck_mgr_ha_3850/configuring_cisco_stackwise_virtual.html

Either case Active switch Hold all the configuration - only some basic config need to join for both the types.

[Joseph W. Doherty]

To be more specific to an OP question, when a switch newly joins a stack, I believe its configuration is replaced by the stack master's.  This is to insure if current stack master fails, any other stack member can continue stack operations.

Remember, a switch stack is one logical device.

If a switch stack becomes partitioned, multiple active logically duplicate devices will be on the network.

[gerdlucyvend22]

Excellent! So a good alternative would be to make the factory default on the switch that will be the "standby", ok!
Another question, to ensure that the master will maintain its settings, should I set it to Priority 15, and the standby set it to Priority 14? Is any additional configuration necessary for stack formation? Another question is, when plugging in the stack cable, is a reboot automatically performed and the stack comes back? Both members reboot or just the standby? I apologize for my ignorance, I am very new to this area of ​​STACK.

[balaji.bandi]

yes if you like switch to be master always when both device boot same time priority kick in.

so master 15, then mebers 14 ...13 ...12 so on.

when it failed from master to slave (once master come back, it stay as slave only - that can not become master - this is failure scenario) to fix you may need to complete reboot of stack.

but the port-number remain same.

[Joseph W. Doherty]

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@gerdlucyvend22 wrote:

Another question, to ensure that the master will maintain its settings, should I set it to Priority 15, and the standby set it to Priority 14?

 No.  Priority setting doesn't have anything to do with maintaining settings.  I just determine "pecking order" when there's a master election.

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@gerdlucyvend22 wrote:

Is any additional configuration necessary for stack formation?

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Depends what you're trying to accomplish.  Often no, but some switch stacks allow you to "pre-provision" a new switch to take the place of a failed switch.

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@gerdlucyvend22 wrote:

Another question is, when plugging in the stack cable, is a reboot automatically performed and the stack comes back? Both members reboot or just the standby?

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No, a stack reboot is not automatic when adding a stack member to a running stack.  I.e. usually, you power on the newly added stack member after it has been cabled to the stack.  Some, though, will connect a running switch to the stack, which I believe, generally isn't recommended.

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@gerdlucyvend22 wrote:

 I apologize for my ignorance, I am very new to this area of ​​STACK.

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No need to apologize, learning is part of the purpose this forum community.

[gerdlucyvend22]

I have a 3850 that I would like to keep its settings, as it is my main switch, how do I ensure that when the stack is built, my main switch will become the master, and keep the configs?

[Joseph W. Doherty]

Simple, power it on first, then wait about 30 seconds before powering on any other stack members.

[gerdlucyvend22]

So to summarize the steps:
1 - Turn on the switch that I want to become the master and keep the settings.
2 - Turn on the Switch that I want to be "standby"
3 - Plug in the stack cable.

Is resetting both "reload" members necessary to form the stack?
I'm a little lost in the step by step.

[balaji.bandi]

There 2 option we mentioned.

1. Either you can do with Switch priority and swith number which you like to be master and standby (in this case if both switches power off and come online, higher priorty switch become master all time.

2. other way if one switch come online that will be master all time, the switch come next become member of the stack. (but if the power off both and on, which ever come first will be master here)

Is resetting both "reload" members necessary to form the stack?  if you making the changes - reload stack to correct the issue always suggested.

[Joseph W. Doherty]

Step 3 first.

First switch to power on for about 30 seconds will become stack master.  Stack masters are not preempted.

When there's no current stack master, there's a stack master election (and if there's only one unit during election, it always "wins").  If multiple switches for election, highest priority wins if only switch with that priority.  If multiple switches with same priority, there may be tie breaker rules (with original 3750s, IOS feature set installed on switch was a attribute considered).

The only way to guarantee master selection is physical power on just the preferred switch first.  Switch priorities work fine if ALL PROPERLY CONFIGURED and all candidates in an election.