Question regarding 3750 Stacks

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May 10th, 2010
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Hi,


I've been reading through the documentation for our Catalyst 3750s an I wasn't quite satisfied with the info I got.  Here's the deal:  We have two stacks of 3750s, one with 5 switches, the other with 2.  Right now I want to move one switch from the stack of 2 (which, I think, is the master switch, as denoted by the * in show version) and put it in the stack of 5.  How can I do this without disrupting service to the network devices on the other switch in the stack of 2, or to the servers attached to the stack of 5?


Thanks!

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Ganesh Hariharan Tue, 05/11/2010 - 00:18
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Hi,


I've been reading through the documentation for our Catalyst 3750s an I wasn't quite satisfied with the info I got.  Here's the deal:  We have two stacks of 3750s, one with 5 switches, the other with 2.  Right now I want to move one switch from the stack of 2 (which, I think, is the master switch, as denoted by the * in show version) and put it in the stack of 5.  How can I do this without disrupting service to the network devices on the other switch in the stack of 2, or to the servers attached to the stack of 5?


Thanks!

Hi,


Check out the below for creation and managment of stack in cisco 3750 switches


http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_example09186a00807811ad.shtml#stack5


and If you want to add a new switch in stack as long as the new switch has the exact same IOS image as the existing stack, the stack will see the new switch. You don't need to power down. As long as you have two stacking cables connecting the first and second switches, removing one of them will not stop traffic. The third switch will adopt the same config as the original stack. You will just need to specify port settings.


Hope to help !!


Ganesh.H


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Michael Hutt Tue, 05/11/2010 - 00:26
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Thanks for the info!  I actually want to take one switch (the master switch, I believe) out of the stack of two.  How will the stack of two deal with losing the master switch?  Will it elect the last remaining switch to be the master and continue operating like normal, or will there be problems?


All the IOS images are 100% identical, btw, so there's no problem there.

hobbe Tue, 05/11/2010 - 04:44
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You state that you want to remove one stack member in a stack of two units thus leaving one unit behind.

As a general rule there is no problem (except murphy´s law) to do that.

what I would do if I where you is to first make a backup of the configuration.

then just power down the switch you wanted to take out, disconnect the cables and of you go.


one small thing about this, this means that if you remove the switch who is number one, the switch numbered number 2 will continue to be numbered 2.

this means that if you want to reach an interface on that switch it would be named gigabitthernet 2/0/1 instead of 1/0/1 wich one would think for a standalone switch.

to renumber switches use the switch command, and that requires a reload.


To install the number 1 switch into the new stack I would first boot it as a standalone and remove all configurations, shut of the power and add the stack cables and start it up.


There is not much to it as such, however try to do this off hours, since murphy sometimes sticks up his ugly head and shit just starts to happen.


Good luck


HTH

Jim Cook Wed, 10/27/2010 - 15:21
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This is an excellent document and was very helpful. Thank you.

vvasisth Tue, 05/11/2010 - 01:07
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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:

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3750/12220se/3750scg/swstack.htm

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.


Regards,

Varun

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