Can I add a switch to working stack of 3750s without traffic interruption?

Answered Question
Sep 28th, 2009

I need to add a third stackable 3750G switch to an existing stack of 2 and was wondering if the first 2 need to be powered down before I install the third?

Do I need to configure the new switch with anything specifically? (aside from assigning ports, etc.)

I'm assuming since I'll have to move around the backend cable, there will be a traffic interruption?

Thanks, Tony

I have this problem too.
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Correct Answer by wyley.johnson about 7 years 2 weeks ago

I typically use tftpd32. it's very simple. You should really use the User Guide for 3750's. You may have to use the archive command if you have downloaded the .tar file. Also, in case you are not aware, you will have to reboot your production switches for the new IOS code to take.

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wyley.johnson Mon, 09/28/2009 - 09:33

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.

ttrevino1 Mon, 09/28/2009 - 11:56

Okay, thanks for the info. I appreciate the help. I plan on configuring it one night this week, so hopefully it will go well. If the new switch has a different IOS, what would I do then?

Thanks, Tony

tprendergast Mon, 09/28/2009 - 13:24

Bring up the switch by itself, upgrade the IOS, do a write erase (to clear config), and then add it to the stack.

You can pre-provision it in the stack to ensure it gets the right priority and all of that jazz by following this section of the doc:

To add a switch, as a slave, to a stack, complete these steps:

Note: Make sure the switch that you add into the stack has the same IOS version as the switches in the stack. Refer to Catalyst 3750 Software Upgrade in a Stack Configuration with Use of the Command-Line Interface to upgrade the IOS in a catalyst 3750 switch.

1.Change the switch priority of the switch to be added to "1".

switch stack-member-number priority new-priority-value

Note: This step is optional, but it will make sure that the switch has fewer chances to become a stackmaster in the future.

2.Power off the switch that is to be added.

3.Make sure that the stack is fully connected so that, when you connect the new switch, the stack will be at least in half connectivity and does not partition.

4.Connect the new switch to the stack with the StackWise ports.

5.Power on the newly added switch.

6.After the new switch comes up, issue the command show switch to verify stack membership.

It should be pretty easy, don't sweat it. If this helps, please rate.



ttrevino1 Tue, 09/29/2009 - 06:42

Thanks for the information, very helpful. I did look at the new config and noticed the only difference I see is the existing switches are C3750-IPBASE-M , while the new switch is C3750-ADVIPSERVICES-K9-M. Will this make any difference (different version?) or can I plug it in without having to clear the config and start over?

Thanks for the help, I haven't done this before and don't want to incur any unnecessary downtime.

wyley.johnson Tue, 09/29/2009 - 07:00

That will make a difference. The IOS's need to be the same. Those are different. The switches do not play well together when there is an IOS mismatch. You can download the proper IOS from the software download section from Cisco.

You really don't need any pre-configuration on the new switch, so you can clear out the existing config on the NEW switch.

The only configuration change that is advisable (as was stated before) is to set the priority level of the second and third switches lower than the priority of the switch you want to be the master.

Ex. Set priority of master switch:

switch 1 priority 15

Set priority of other stacked switches:

switch 2 priority 1

switch 3 priority 1

This puts a higher weight on the MASTER switch to stay the master if there is a reboot.

ttrevino1 Tue, 09/29/2009 - 07:23

Okay, thanks everyone for the help. I'll work on reconfiguring the switch, then go plug it in and work on the remainder of it later this week. Thanks for the assistance.

ttrevino1 Thu, 10/01/2009 - 11:56

Okay, so I was able to download the latest version of the IOS for this switch and now need to upload it to the switch. I'm trying to use M/S's IIS service for ftp, but I have to log in with an ID and password in order to connect to the ftp server. When I get into the config of the switch, I use the command "copy ftp startup-config", then enter the IP of the server (local machine), destination, etc. However, it keeps failing because there is never a prompt for the ID or password. Is there something else I should be doing to get this to work properly? Is there a better ftp program to use, as I'll have to upgrade the switch versions I'm attaching this switch to, as well as other switches in the near future.

Thanks again for the help.

Correct Answer
wyley.johnson Thu, 10/01/2009 - 12:27

I typically use tftpd32. it's very simple. You should really use the User Guide for 3750's. You may have to use the archive command if you have downloaded the .tar file. Also, in case you are not aware, you will have to reboot your production switches for the new IOS code to take.

ttrevino1 Mon, 10/05/2009 - 13:06

Thanks for all the help. I was able to get this running using this tftp server software and all the advice!

Have a great day and thanks for the help, Tony

uzair syed naveed Tue, 10/06/2009 - 03:55

Try 3CDaemon software to handle your TFTP / FTP needs, I find this s/w pretty usefuls as it even helps u simulate a syslog server using this.


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