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Answered Question
Mar 26th, 2010


I successfully stacked 2 3750's and they have been fine for a few months.  I used a stack cable from stack port 1 to stack port 1 on the other switch, but today I was told that is wrong it should go from stack port 1 on one of the swithces and connect to stack port 2 on the other, is that right?

I have this problem too.
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Correct Answer by Aaron Harrison about 6 years 10 months ago


Yes, just refer back to that document I posted earlier... as long as you are creating a loop, it's fine.


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Overall Rating: 5 (1 ratings)
Aaron Harrison Fri, 03/26/2010 - 04:45

When you buy a 3750, you get  a 50cm stack cable with it.

So you have two switches now, do you have two cables connecting them?

I.e. port 1 to port 1, port 2 to port 2?

If so, you just disconnect the port2 cable, and work the third switch into the pattern.

It's easier to get your head around if you cable Sw1 Port2 --> Sw2 Port1, Sw2 Port2 --> Sw3 Port1, then Sw3 Port2 --> Sw1 Port1, but other configurations work fine.

Aaron Harrison Fri, 03/26/2010 - 05:09

I see..

Then you can add a third switch by connecting it to any available port.

What you don't have is resilience... and half of your bandwidth.

You should pick up another cable from somewhere and put it in.



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Andy White Fri, 03/26/2010 - 06:32

Thanks I will pick up another stack cable, so port 1 will go into port 1 and port 2 into port 2, would that be ok?  Then there would be no downtime as I don't have to unplug the current stack cable.

Aaron Harrison Mon, 03/29/2010 - 01:57


Sure - just make sure you don't disturb the existing cable. They're not always screwed in as well as they should be.



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Andy White Mon, 03/29/2010 - 02:02

Thanks for your quick reply, there maybe a chance i need to add a 3 switch later in the year.  At the moment I will just have 2 switches with stack port 1 & 2 into the same ports on switch 2, I guess I will have to mix things up in a 3 switch scenario?


Correct Answer
Aaron Harrison Mon, 03/29/2010 - 02:11


Yes, just refer back to that document I posted earlier... as long as you are creating a loop, it's fine.


Scotland1314 Mon, 03/29/2010 - 04:02

I am having a similar problem. I have two stacked 3750G 48 port switches working well. I tried to add a 3rd 3750 G 24 port and it wouldn't work at all. The error I originally made was I configured an IP for VLAN1 on the 3rd switch which confused the master no end !!. Removed that and did a reload, still not working. They are running slightly different IOS versions the 48 porters are 12.2 (25) Se3 and the 24 port is 12.2 (35) Se5, can anyone suggest a solution please ?, this is a high level project and I need to get it working. All help appreciated thanks.


Aaron Harrison Mon, 03/29/2010 - 04:32


1) Switch the new switch off

2) Connect it to the stack

3) Power it up

4) Connect to the existing switches in the stack by telnet or console into one of the original switches, and do a 'show switch'. You should see it listed with it's current status. Let us know what the status is and post back the output.

Also post back the 'show version' output.

Likely it hasn't copied the software over - when adding to the stack they all need to be on the same version.

You can use 'archive copy-sw' to force the software on to the new switch.



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Andy White Mon, 03/29/2010 - 04:34

How have you got your stack cables, how have you provisioned them, they should be the same ios.

Scotland1314 Mon, 03/29/2010 - 04:40

Cheers for the help Aaron and Andy, the IOS version on the new 24 port switch is 12.2 (35) the existing 48 port ones are 12.2 (25). The stack cables are copied from an existing working 3 stack setup funnily enough two 48 porters and the 3rd a 24 porter. I will check and see the versions that they are running to see if they are the same. I Didn't do the original config for the 48 port switches, all I did was make them manage via SNMP and telnet etc, as they were in a VERY basic mode when I arrived in sunny Libya !!! not even an enable password had been set, handy for management and troubleshooting or what ? Edit, just checked the Working stack (2x48 port + 1 24 port) and they are all on the same IOS version. Is their any way to downgrade the new 24 porter I put in so as to not cause to much network disruption as I think it would cause if I upgraded the 2 48 port switches ?


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