switch problem with stacking.

Unanswered Question
Dec 15th, 2009


    i'm facing very serious problem regarding stacking between cisco 3750 switches:-

We have two cisco 3750G (48 port) and this new cisco 3750 (24 port).Both switches are unconfigured.When we connect stacking cable between them, then First switch(cisco 3750-48 port) restart again and again within short period automatically.Stacking LED is not glowing.It means stacking is working between both switches.
              We have checked stacking cable.Its working properly.
              Kindly help me in this matter as soon as possible.This is very urgent.
              Waiting for your reply soon.



I have this problem too.
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Leo Laohoo Tue, 12/15/2009 - 01:35

When stacking two or more 2975/3750/3750E together, follow the simple rule-of-thumb:

1.  All stack members MUST have the same IOS version and IOS feature set; and
2.  When adding stack members to the stack, always cable up the stacking cable FIRST before applying power.

It sound like you powered up both stack switches and cabled up.  One switch went into master and the 2nd switch reloaded and either the IOS got corrupted or the IOS version/feature is not the same.

siddindia Tue, 12/15/2009 - 02:33

Hi Leolaohoo,

                     I have checked in both switches of IOS.IOS of both switches are same and we are activateing power of both switches after attaching stacking cable between both switches.

                     Till now, we are facing same problem.


vvasisth Tue, 12/15/2009 - 02:52

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I understand that you require instruction on how to add a new cat3750 to an existing stack.

First off, if a new switch needs to be added, it must have the same IOS image version as that of the existing 3750 in the stack. This avoids the version mismatch issue. To do so, the new switch to be added must already have the image loaded to it same as the ones on the stack.

This link has all necessary procedures when managing switch stacks:


One important note though, make sure the switches that you add to or remove from the switch stack are powered off.

This is because:

Adding powered-on switches (merging) causes the stack masters of the merging switch stacks to elect a stack master from among themselves. The re-elected stack master retains its role and configuration and so do its stack members. All remaining switches, including the former stack masters, reload and join the switch stack as stack members. They change their stack member numbers to the lowest available numbers and use the stack configuration of the re-elected stack master.

Removing powered-on stack members causes the switch stack to divide (partition) into two or more switch stacks, each with the same configuration. This can cause an IP address configuration conflict in your network. If you want the switch stacks to remain separate, change the IP address or addresses of the newly created switch stacks. If you did not intend to partition the switch stack:

a. Power off the new switch .

b. Reconnect them to the original switch stack through their StackWise ports.

c. Power on the switch.

I hope this link would be helpful.




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