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We have a switch stack with six Cisco 3850 switches in it and for some reason the physical order of the switches in the cabinet and the switch number are not in sync. This is causing confusion; when an engineer physically plugs a port into switch 3 they have to remember to configure interface Gi6/0/x instead of G3/0/x.

My experience of renumbering switches is that it requires a reboot to take affect. Given that stack switch supports a 24/7 operation, arranging downtime will be hard and could take several months. However the area is often prone to power-cuts. Is there any reason why I shouldn't just change the switch numbers now and if the switches go down due to power issues before we can reboot them in a change window, they will reboot with the correct numbers?

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    I'd try stickers...
    – Zac67 ♦
    Commented Feb 3, 2023 at 13:08
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    "This is causing confusion; when an engineer physically plugs a port into switch 3 they have to remember to configure interface Gi6/0/x instead of G3/0/x." Are the labels wrong, or can the tech not read?
    – Ron Maupin ♦
    Commented Feb 3, 2023 at 13:17
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    .. and then there's even the mode button on many stackable ciscos, which helps to identify the switch number in the stack.
    – Marc 'netztier' Luethi
    Commented Feb 3, 2023 at 14:47
  • We have a lot of stacks, lets say 80, 79 of them go 1,2,3,4,5,6. We have one stack that goes 1,2,6,4,5,3. The network team are not the only team responsible for patching so the significance of a sign highlighting this discrepancy would be lost on them. Why train people to remember this discrepancy when I could just renumber the switches, I'm just asking if there are any issues with my plan.
    – The Footsie
    Commented Feb 3, 2023 at 15:32

2 Answers 2

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Frame challenge

You state that: "stack switch supports a 24/7 operation, arranging downtime could take several months."

In this case you, surely your setup can support the failure or maintenance of a switch without impacting operations?

Otherwise:

  • how do you perform maintenance (OS upgrades...) on your systems?
  • what is you BCP - Business Continuity Plan- in case of a switch failure?

You should first correct the setup so the downtime of a switch, for whatever reason, doesn't have any impact. This is much more important than having the switch stacked in the correct order. And once this is done, you'll be able to re-number it without impact.

There's an adequate solution for most cases to provide fault-tolerance to the running systems - the most obvious being LAG/PortChannel.

Also if you have engineers that don't double check which ports they are configuring, you have other issues to tackle. For example: a

  • are unused port in the shutdown state?
  • do you have a description set on all ports?

Finally if a power outage in the building also impact your network, that means you don't have an UPS. Once again, how can you support 24/7 operations with such a setup?

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  • I appreciate the answer, I would say 'welcome to a beleaguered public health service'. We are having to support 24/7 services but without the budget, often now since Covid in buildings that are not suitable for walk-in emergency centres. OS updates very hard to arrange, BCP in this instance isnt my issue, if there are power issues to the building that last beyond the UPS uptime then there is not much I can do. All ports run back to the same comms room so any redundancy wouldn't survive the power outage.
    – The Footsie
    Commented Feb 3, 2023 at 18:34
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    Regarding the issue being the fault of tech not listening I disagree - If I went on workplace.stack and asked ‘I have 80 switches, 79 are configured one way, one is configured a different way, I have tried to explain the situation but confusion still happens occasionally. How do I get staff to understand?’ the first comment would be ‘why not bring the switch in line with the other 79?’
    – The Footsie
    Commented Feb 3, 2023 at 18:36
  • Maint window is only once a year? (been many places like that.) BCP for any failure is commonly "RUN" - fix it as fast as humanly possible. (i.e. you have on-site spares of important equipment. I've been there many times... it rarely works.)
    – Ricky
    Commented Feb 6, 2023 at 22:09
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If it is really that big a problem, do the reconfiguration and just unplug the power cable and plug it back in afterward. Power outage. There you go. If they are that frequent then there is no issue, right?

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    That doesnt work. Power cuts affect the whole building, pulling the power to the switch will only affect the switch. Explaining that one away while also being in the comms room at same the time would be tough.
    – The Footsie
    Commented Feb 3, 2023 at 15:42
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    "Dang! Plug fell out." :-)
    – Ricky
    Commented Feb 6, 2023 at 22:05

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