How to stack two Cisco 3750 switches

Posted on 2009-07-02
Last Modified: 2012-05-07
Hi All

I have an existing 3750 on our network which is full and a new 3750 has been bought with the intention of stacking it onto the full one. We have never done this before and are a bit unsure of the steps. I have read the stacking section of the 3750 config guide and a lot of the posts on here but I'm still confused.

Existing Switch = Stack 1, New Switch = Stack 2

Stack1 1 has an IP address, tacacs setup, password, 2 vlans in use and is running IOS ver 12.2(25)SEB4
Stack 2 is brand new out of the box with no config changes and is running IOS ver 12.2(35)SE5

From what I read both IOS versions have to be identical. Does this mean Switch 1's IOS has to be upgraded?

DO I need to setup a local password, rename Switch 2 etc, or will the switch only be accessible via the stack IP address. My fear is that someone could just plug a console cable on and have no password etc.

If someone could just give me the steps I need to complete to get this going I would be most grateful.

Question by:darran_d
LVL 29

Expert Comment

ID: 24763470
You should keep the IOS up to date no matter what you are doing with them,...and it is always a good idea to keep them on the same versions.
If you just simply connect a patch cable between the two switches you have effectively "stacked" them,...but different manufactures may pile other "stuff" onto the definition of the word.  I don't own or have experience with your specific model of switches but we have had some in the past that has special ports that required a special cable (purchased separately) that was used to link them together.  You powered them off,..connected the cable,...powered them on,...WaLa! ,...they were stacked.  But others we have just have a Gigabit module (the switch is normally only 100mbps) that you add to each switch and connect it via them with a short patch cable capable of gigabit speeds.
Switches are Layer2 Devices,...IP# are irrelevant in this particular context.

Author Comment

ID: 24764215
Yeah I have the stack cable for rhe new switch. The switch running the lower IOS is the live switch so I need to keep that up if possible.

So are you saying that I can just plug in the new switch via the stack cable and that should be it?

LVL 29

Expert Comment

ID: 24764395
You can double check with the Cisco docs to be sure but what I would do is bring the IOS up to date and have all of them on the same version. When you do that update you will have to power cycle the older switch so that would be a good opportunity to connect the stacking cable to the two switches while they are powered off.  When you power them up it should now be stacked.
I would thnk that this would be all there is to it.  They would probably be fine even if the IOS versions did not match,...but you might as well get that taken care of in the process as you do this.
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Expert Comment

ID: 24765689
Don;t just jump to latest IOS, There is IOS bug tool kit to make sure least porblems. Also if you are going to upgrade make sure to have copy of your old IOS, Config backup.

Expert Comment

ID: 24770570

Cisco StackWise is the solution to stack 3750 switches together (CAB-STACK-50CM= , CAB-STACK-1M, CAB-STACK-3M as you can see there are 3 different lengths).

If you don't experience network problems, you don't have to upgrade your switches to the latest IOS version. It is enough to run the same IOS on both swithes.

The easy way to backup/install IOS on the switches is to use the GUI. you need to confiugre the switch (enable http in the global config mode).

After this procedure you will be able to connect to both switches with a sinle IP address. the GUI is cool.

Good Luck!
LVL 16

Accepted Solution

Aaron Street earned 250 total points
ID: 24772112
you dont neeed the latest version, nither do you need the two to be identical,

they do both need to be the same major version!!

so verion 12. something

it is also best to have same minor versions ie. 12.45(something)

if the have the same major and minor version when you join the switch to the stack they will automaticaly upgrade / downgrade to the maser switch exact version.

if after they have booted you do a

#show switch

ansd see an entrey saying

#switch version mismatch.

then as long as you have the same major version you can do a

#archive download-sw /destination-system

and give a switch number. this will over write the IOS on the specified switch with the one on the current master. a lot simpler than upgrading the switch before adding it to the stack..


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