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Cisco stacked 3750 switch

Posted on 2011-02-28
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Last Modified: 2012-05-11
Hi,

I have a stacked Cisco 3750 switch, two of them in this stack.  They have dual power to a Cisco 2200 redundant power unit.  It appears (according to tac) that the on board power unit on the second switch in the stack has failed, and the 2200 is what is keeping it up and running.  They told me the onboard power supply is not hotswappable, and the second switch in the stack must be replaced.  

What is the best way to do this ?  Do I shut down both switches, swap out the second switch, plug cables back in and power up ?  Do I just shutdown the second switch with the failed power supply, pop in the new one, plug in cables and power up ?  The cfg is on the first switch in the stack correct ?  Is there anything I need to pull off of the second switch ?

Thanks
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Question by:Elemental12
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Expert Comment

by:eeRoot
ID: 35000143
If the switch with the failed power supply is NOT the stack master and is NOT the switch with the network uplink to the rest of the network, then you can replace it while leaving the primary switch up.  In a stack, the config is stored on all switches and synchronized automatically whenever there is a config change.  When the new switch powers up, it will inheret the config from the master switch.

Also, it would be a good practive to make sure that the new switch has the same firmeware version as the switch it's replacing.
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aleghart earned 333 total points
ID: 35000279
^ second that.  If the firmware levels do not match, you may end up with a brick.  The master may attempt replacing firmware.  If it is writing old over new...brick.  If it is writing new over old, but stalls/fails...brick.

Better to do the firmware upgrade offline, while the existing stack units are still functioning.
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Author Comment

by:Elemental12
ID: 35000742
ewww ... Very nice thought guys, I did not even think of the firmware between the two.  I will add that to the list.  Dumb question, but what is the cmd to find out which one is the master ?

Thanks
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Author Comment

by:Elemental12
ID: 35000882
show ver showed me :



Switch   Ports  Model              SW Version              SW Image
------   -----  -----              ----------              ----------
*    1   52     WS-C3750G-48TS     12.2(35)SE2             C3750-IPSERVICESK9-M
     2   52     WS-C3750G-48TS     12.2(35)SE2             C3750-IPSERVICESK9-M
 
So i assume the top switch is the master.  I am going to confirm by comparing ints plugged in (ie, if g0/1 in switch 1 is active, and g0/1 in switch 2 is inactive, and I go down there, and the top switch has something plugged into g0/1, then I know the top one is the master).  And as Cisco says switch 2 is the one with the failed power supply, then I know the bottom one is the one to swap out ...
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Assisted Solution

by:kdearing
kdearing earned 167 total points
ID: 35001419
A stack automatically updates all switches to the same version.

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_25_see/configuration/guide/swstack.html
"All stack members are eligible stack masters. If the stack master becomes unavailable, the remaining stack members participate in electing a new stack master from among themselves. A set of factors determine which switch is elected the stack master. One of the factors is the stack member priority value. The switch with the highest priority value becomes the stack master."
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Author Comment

by:Elemental12
ID: 35001483
Ok, so I confirmed which physical switch is switch 2.  Once it shows up, I will check the version and downgrade accordingly.  Anything else I need to keep an eye out for ?

Thanks
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Assisted Solution

by:aleghart
aleghart earned 333 total points
ID: 35001664
In general, watch cable position.  Label them accordingly before disconnecting.  When you unplug them, all ports may not be equal.

For instance, did you have one forced to 10Mb duplex, or aggregated with other ports.

When replacing, I was able to move the downed switch 2u down, and mount the replacement.  Then I could move the patch cables over one-by-one.

YMMV.  But it made it easy that I could replicate the cable layout and not have to change any notes or documentation.
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Author Comment

by:Elemental12
ID: 35007011
Thank you for the suggestion of racking first ... Unfortunately, there are items above and below, so I cannot rack ahead of time, but I can label the interfaces before I pull them so I can put them back in the same port on the new one.

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