Replacing Switches in Cisco Switch Stack

aquilla

Afternoon,

I'm posting to check that I haven't missed anything in my plan.

I have maintenance window coming up whereby we will be swapping a number of switches in a couple of 2960 stacks due to a hardware fault identified by TAC:

* Stack 1 - 6 switches (swapping 5)
* Stack 2 - 2 switches (swapping both)

I spoke with my TAC engineer about the best way to approach this and he simply pointed me at the Cisco page for managing switch stacks. I've read through the document but there isn't (that I can see) a great deal on replacing switches in a stack. I put together a plan and asked my TAC engineer to review it but it fell on deaf ears.

So I'm asking if some kind person can review and let me know if they see any issues.

In the 6-switch stack we will be replacing switch 1 to 5 (priority 15,14,13,11,10). Switch 6 will not be replaced and has a priority of 1. My plan for this stack (proposed to TAC) is:

- Backup running configuration and vlan.dat
- Change priority of switch 6 (not being replaced) to 15;
- Change priority of switch 1 to 9;
- Save the configuration;
- Reboot stack to ensure new master is re-elected?
- Power down switch 1 and remove from rack;
- Prep replacement of switch (pre-load correct IOS);
- Rack new switch, connect stack cables and power on;
- Check switch has joined the stack properly and downloaded the config;
- Repeat for switches 2 - 5;
- Once all switches are replaced, revert the switch priorities of switch 6 and switch 1;
- Save and reboot switch 6 (force re-election).

Here are my questions:

* When you unbox a new switch (with stacking capability), it has the line "switch 1 provision <model>" in the configuration. Will we need to amend this (via the "switch 1 renumber x" command) as part of the prep work before connecting the switch back into the stack? For example, when replacing switch 5 will it be enough to leave it as the default or will we have to do "switch 1 renumber 5" before connecting to the stack or will the stack automatically recognise this is the replacement for the missing switch?

* Does the mac address field (in the "show switch detail" output) have any bearing or is it just for reference?

I have some 3750s at home and plan to carry out some testing later this week but would be grateful for any advice from anyone that has done this before. Unfortunately I haven't had much exposure to switch stacks hence my questions.

Thanks in advance.

Queue

Switch with lowest MAC= Master then continues on for standy.

I would make sure all switches share the same code. Do this with a USB/tftp server prior to adding them to the stack.

For the switch you will keep update/downgrade the code. Add another switch to make a stack with same code. Set the priorities to make sure they don't lose master/standy election. Then just add switches with same code version and it will continue to build the stack. The config from the master switch you started with will be downloaded by all the switches to be added. You will not have to worry about the switch provision ****. Then use the switch 1 renumber 2 ... afterwards and write mem then reload to make it physically correctly numbered in the rack.

This has worked for me on over 170 switches for a refresh project I completed. They were 3850 access switches.


You will see my process is exactly (yours better typed up) what you have in mind.

Your questions: the switch ... provision does not have to changed. The only time this has been an issue is if you re-use a switch because it was provisioned at one time with a previous number. So even if that re-used switch was switch 4 in a stack and you want it be to switch 3 it will be provisioned as switch 4. Then you just re-provision it correctly no big deal. The MAC is of no importance if you force the election (I believe).

aquilla

Thanks.

I'm going to be doing some testing today on some 3750s I've got.

TechGromit

If possible arrange the switches by MAC address (low to high) in the order you want them to be in the stack. It's a lot easier to do it this way then to have to renumber them later.

TechGromit

aquilla wrote: »

* When you unbox a new switch (with stacking capability), it has the line "switch 1 provision <model>" in the configuration. Will we need to amend this (via the "switch 1 renumber x" command) as part of the prep work before connecting the switch back into the stack? For example, when replacing switch 5 will it be enough to leave it as the default or will we have to do "switch 1 renumber 5" before connecting to the stack or will the stack automatically recognise this is the replacement for the missing switch?

* Does the mac address field (in the "show switch detail" output) have any bearing or is it just for reference?

When there is no Priority order is specified the switches are arranged by Mac lowest to Highest.

Renumbering switches can be a real pain in the butt. In the case where you have switches number 1 thru 5, and you have to change the order, you have to renumber switch 3 to switch 6, so you can then renumber switch 5 to be number 3, then go back and and renumber switch 6 to switch 5. This will take two reboots for everything to come up in the order you want.

Queue

@TechGromit.

You can renumber the whole stack and write memory and reload once.

Say you have a stack of 6.

This is the logical order from top down
1
2
6
4
3
5
You go push the button on the switch see this write it down or record it. Now write in another column the way you want it numbered.
1
2
3
4
5
6
Match those up next to each other and start renumbering: In exec mode
switch 6 renumber 3
switch 3 renumber 5
switch 5 renumber 6
write mem
reload
confirm

aquilla

So I did some testing this afternoon with 3 x 3750s I have here. First off I built a stack using all three and set the master to a priority of 15, second switch to a priority of 10 and third to a priority of 5.

First I powered down switch 2, disconnected the stack cables and then bought it back up and wiped the configuration on it. Made sure its switch priority was 1, no other switches were provisioned in its configuration and left it with a blank configuration. I then powered it down, reconnected it back to the stack. As expected switch was re-added to the stack and the configuration applied. Once it was back in the stack I manually adjusted the priority of the switch back to 10.

Next I tested replacing the master. I changed the priority of the master (switch 1) to 9 and made switch 3 the new master by upping the priority to 15. Saved the configuration and rebooted the stack. Verified that switch was the new master and then powered down switch 1 and disconnected the stack cables. Again did a write erase and deleted the vlan.dat on the now-isolated switch. Made sure the priority of the "replacement" was 1. Powered device off, reconnected to stack and powered on. Switch successfully added to stack and config downloaded. Changed priority back to 15 and dropped switch 3 back to 5, rebooted the stack and confirmed all OK.

If the 2960's behave the same as the 3750's then I don't expect any issues.

Thanks,