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Convert Cisco 3750 to Stack - No downtime?
I want to convert from a single switch to a stack. Easy enough to do but I was curious if I could do it without any downtime. Here is what I have. I have a single Cisco 3750 (Switch 1) that a bunch of servers are hooked up to. I have another Cisco 3750 (Switch 2) that I just added to the rack which doesn't have anything plugged into yet. I have both ready to configure into a stack. Both are essentially running as Stand Alone Masters right now.
So given that all the servers are connected to switch 1, can I hook up Switch 2 with a Stack cable, boot it up, and allow it become part of a stack? And would Switch 1 remain up without dropping any connections or require a reload?
So given that all the servers are connected to switch 1, can I hook up Switch 2 with a Stack cable, boot it up, and allow it become part of a stack? And would Switch 1 remain up without dropping any connections or require a reload?
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I would advise that you make sure that the new switch is running the same version of code as the existing switch. If you don't the switch will boot and give a version mismatch error. Depending on the version of code on the new switch you may be able to auto-upgrade from the existing switch (or downgrade as the case may likely be) but that can fail and may cause your stack to reload in come cases.
What Robert said about turning off the new switch is important, as he said. If you add the switch to the stack while it's powered it may cause the existing switch to reload and then elect itself as master. That could cause your port configuration to become incorrect.
What Robert said about turning off the new switch is important, as he said. If you add the switch to the stack while it's powered it may cause the existing switch to reload and then elect itself as master. That could cause your port configuration to become incorrect.
ASKER
So, to clarify
Both switches have the exact same system image loaded. I upgraded both to the most recent version to prepare them for Stacking already. Since every server connected to the switch uses network teaming, I was able to get switch B running with a stand alone config, move all the 2nd network cables for every server to it, wait for the team to come back up, then disconnect switch A from each server. That allowed me to load the new image on each switch.
So right now, each server is actually connected to each switch, one port on each server to each switch and the network team works. I can turn off either switch and all the connections still work just fine for each server. So knowing that, I can just power off the switch that I don't want to be the master, connect my stack cables, and then power up the switch. Sounds like that switch will see it has a Master and become part of the stack but I will adjust the priority before shutdown and stack connection just to be sure.
Both switches have the exact same system image loaded. I upgraded both to the most recent version to prepare them for Stacking already. Since every server connected to the switch uses network teaming, I was able to get switch B running with a stand alone config, move all the 2nd network cables for every server to it, wait for the team to come back up, then disconnect switch A from each server. That allowed me to load the new image on each switch.
So right now, each server is actually connected to each switch, one port on each server to each switch and the network team works. I can turn off either switch and all the connections still work just fine for each server. So knowing that, I can just power off the switch that I don't want to be the master, connect my stack cables, and then power up the switch. Sounds like that switch will see it has a Master and become part of the stack but I will adjust the priority before shutdown and stack connection just to be sure.
If you want the top switch to be stack master, power it on first and wait 10 seconds or more before powering on the second switch.
You probably want to connect Stack 1 port to Stack 2 port. However there are numerous configurations possible so i would suggest downloading the Catalyst 3750 Switch Hardware Installation Guide:
http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/hardware/installation/guide/3750hig.html