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New Member

Removing 4 out of 6 switches in a switch stack

Hi all,

A very simple question for the group (I hope!) regarding 3750 switch stacks.

I've inherited a stack of 6 3750 switches.  I need to reduce this to two.  All of my active connections have been moved over to the remaining two switches I plan to keep.

Here is the output of the show switch

DASW01_4STACK#sh switch

Switch/Stack Mac Address : 001c.b1d9.cb80

                                           H/W   Current

Switch#  Role   Mac Address     Priority Version  State

----------------------------------------------------------

1       Member 0019.2f07.ab80     1      0       Ready              

*2       Master 001c.b1d9.cb80     1      0       Ready              

3       Member 001c.b1e1.5d80     1      0       Ready              

4       Member 001c.b1f6.4a80     1      0       Ready              

5       Member 0023.eabd.3500     1      0       Ready              

6       Member 001c.0ea1.be80     13     0       Ready   

The two switches I want to keep are # 5 and #6.

As you can see, for some reason the master is not on switch 6 even though it has the highest priority.  All the switches are connected together with the proper redundant stack cables.

I've never worked with stacks before but would the actions be as simple as.

1. Backup configs!

2. Turn off switches 1 to 4 one at a time an allow for the stack to stabilize after each switch is powered down.

3. Verify that switch 6 is now the master and everything still works.

4. Turn off switch 5 & 6 and connect the stack cables of each switch to each other for redundancy (currently only one cable connects switch 5&6)

5. Turn on switch 5 & 6

Am I missing anything?

Thank you!

-Pete

Everyone's tags (2)
12 REPLIES
Green

Removing 4 out of 6 switches in a switch stack

Peter,

Loads of tips in this doc:-

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

Regards,
Alex.
Please rate useful posts.

Regards, Alex. Please rate useful posts.
Super Bronze

Re: Removing 4 out of 6 switches in a switch stack

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

You could leave switch 6 "on".  It's okay to make stack connections as long as one side is off.

I don't see a need to wait between turning off switches.  Just turn of switches 1 to 5, cable just 5 and 6, turn 5 back on.

New Member

Removing 4 out of 6 switches in a switch stack

Thanks so much for the information guys.  Seems straightforward enough. 

I will plan for some downtime and see how it goes!

-Pete

Hall of Fame Super Gold

Re: Removing 4 out of 6 switches in a switch stack

1. Backup configs!

It won't work.  Let me explain ...

You plan to use switches 5 and 6?  Ok, guess what is the interface naming convention?  It's going to be "interface 5/0/XX" or "interface 6/0/XX".

You want them to be 1 and 2 right?  So here's how it goes:

1.  No need to backup the config because they are wrong;

2.  Run the following command for switch 5:

config t

switch 5 renumber 2

end

wr

3.  Run the following command for switch 6:

config t

switch 6 renumber 1

end

wr

4.  Power down the switches you do not need.

5.  DO NOT REMOVE the stacking cables just yet.

6.  Issue the command "reload" to reboot 5 and 6.  Once 5 and 6 reboots, they'll become switches 2 and 1.  Make sure your interface configurations are correct.

7.  Remove the stacking cable one-at-a-time.  Make sure there is at least a single stacking cable connecting 5 to 6.

8.  Issue the "switch X priority NN" command to both 5 and 6.

9.  Remove the configuration for the switches removed using the command "no switch X pro ".

Done.

Super Bronze

Re: Removing 4 out of 6 switches in a switch stack

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

Leo Laohoo wrote:

1. Backup configs!

It won't work.  Let me explain ...

You plan to use switches 5 and 6?  Ok, guess what is the interface naming convention?  It's going to be "interface 5/0/XX" or "interface 6/0/XX".

You want them to be 1 and 2 right?  So here's how it goes:

Sure it will work, assuming continuing to use existing stack numbering (although I think renumbering them is a great idea).

1.  No need to backup the config because they are wrong;

Although switches shouldn't lose config even when powered down, it never hurts to have a saved configure.  Assuming some how the config got totally whacked, you'll want that saved copy.  Regarding "they are wrong", even if you want to renumber, you could take a copy of of the save config and with any editor renumber the ports.  Having a copy of the config also preserves everything else in the config.

Oh, something else you may want to back up, the VLAN database if running VTP in server or client modes.

7.  Remove the stacking cable one-at-a-time.  Make sure there is at least a single stacking cable connecting 5 to 6. 

8.  Issue the "switch X priority NN" command to both 5 and 6.

When do you recable the second cable between the (original) 5 and 6?  You would recommend connecting the cable while both units are powered?

Hall of Fame Super Gold

Removing 4 out of 6 switches in a switch stack

When do you recable the second cable between the (original) 5 and 6?

There is already an existing cable connect the two.  So once switches 1 to 4 cable have been removed, there should be another cable left.

You would recommend connecting the cable while both units are powered?

As long as you have a single cable connecting 5 and 6, you can re-cable while the two units are powered up.  I've done this job so many times. 

Super Bronze

Re: Removing 4 out of 6 switches in a switch stack

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting


You would recommend connecting the cable while both units are powered?

As long as you have a single cable connecting 5 and 6, you can re-cable while the two units are powered up.  I've done this job so many times. 

I don't doubt you that you've done this many times without issue, but to quote Cisco:

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

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

Hall of Fame Super Gold

Removing 4 out of 6 switches in a switch stack

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

But Joseph you are not ADDING switches.  You are REMOVING switches from a stack and re-cabling.

If one was adding a new switch, then yes, I recommend the new switch is to be powered OFF before connect the stacking cable. 

Super Bronze

Re: Removing 4 out of 6 switches in a switch stack

Disclaimer


The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.


Liability Disclaimer


In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.


Posting

 

Leo Laohoo wrote:

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

But Joseph you are not ADDING switches.  You are REMOVING switches from a stack and re-cabling.

If one was adding a new switch, then yes, I recommend the new switch is to be powered OFF before connect the stacking cable. 

Leo, an excellent point!

Powering of the switch, when "adding" to the stack, no doubt gets it to initiate itself as a stack member.

Re-cabling existing stacks members, shouldn't need that, but the question then is whether the hardware (stack connections) were designed for making "hot" (i.e. both sides powered on) connections.  If they are, then you're correct, no need to power off switch 5.

New Member

Removing 4 out of 6 switches in a switch stack

Thanks for the additional info, I wasn't planning to renumber them but may do so now.

I'm very happy I to have found this fourm and will work to pay it forward.

New Member

Re: Removing 4 out of 6 switches in a switch stack

Just a quick update.

I powered down 4 of the 6 switches last night with no issues.  There was a 30 second delay when the master (#2) was shut and the new master (#6) took over.  I was knocked out of my telnet session and needed to log back in.

Unknown to me, I had a SonicWall FW device that was using the Layer-3 VLAN interfaces defined on the stack as a default gateway.  When the master moved, I guess the MAC address changed and the firewall didn't get the update.  I had no way to force an arp cache update.

A reboot of the Firewall this morning solved that issue.

The next step will be to clean up the stack cables.  I'll probably power off the remaining two switches just to be safe.

Super Bronze

Re: Removing 4 out of 6 switches in a switch stack

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Unknown to me, I had a SonicWall FW device that was using the Layer-3 VLAN interfaces defined on the stack as a default gateway.  When the master moved, I guess the MAC address changed and the firewall didn't get the update.  I had no way to force an arp cache update.

Yes, that's expected default behavior.  There is a 3750 command to preserve gateway MACs when master changes.  Another way to avoid it, is to use HSRP for gateway IP (even when there are no other HSRP gateways).  You might want to use one or the other, so an unplanned outage of your master doesn't hang FW again.

When master changes MAC, I think I recall, new master will send out a gratious ARP, but not all clients will process it.

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