How to arrange the 3750 stack cables effectively

Unanswered Question
Mar 16th, 2009

Hi all


Attached is a pdf diagram showing I've stacked together 4 x Catalyst 3750 switches. It's working fine at the moment but if the power to one rail is lost, the complete stack is broken. Hence I thought of moving the power connection in the 'New Setup' to make it better. This kind of taking care of the power rail issue but even in the new setup, it is still possible to break the stack should two of the switches fail at the same time (eg switch1 and 3 or switch2 and 4). I just wanted to know whether my stack cables are in the most effective position and there's little I can do if the switches fail at the same time (as mentioned). I've already taken into consideration of using RPS.


Thanks in advance for your help.

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glen.grant Tue, 03/17/2009 - 04:34

The way to wire them is to go from port 1 on the top switch to port 2 on the next switch all the way down the stack until the bottom at which point you will wire port 1 on the bottom switch to port 2 on the very top switch . This will give you the redundancy you require . The likelyhood of 2 switches failing at the same time it very remote and nothing you have any control over. PS there is no pdf attached to your post so we couldn't look at it .

Joseph W. Doherty Tue, 03/17/2009 - 05:50

Since you have two power rails, one or two UPSs in the rack might be an option.


Plug switch A into rail 1, plug switch B into rail 2, plug switches C and D into UPS and plug UPS into either rail 1 or 2 (let's assume rail 2.)


Rail 1 fails you lose switch A. Rail 2 fails you lose switch B and UPS now on battery. Switches C and D okay until UPS battery runs down or you replug UPS into other rail.


PS:

With two UPSs, you could run C and D on their own (more UPS battery time), or run two on each UPS, one UPS per rail. No switch (initially) down with latter.


You could also run all 4 switches on one UPS, but UPS battery will drawn down faster, although you, again, don't (initially) lose any switches.


Possible issue with RPS, recall you need to boot 3750 switch to get it back on primary power(?).

vincent-n Tue, 03/17/2009 - 15:25

Went home last night and realised that I forgot to include the PDF diagram. Please see attached.


How about this setup then.


- Using the new setup, I could use a single RPS unit to power up all 4 devices. I understand that the RPS can support max 2 switches at the same time but that should rule out the possibility of two switches failed due to power at the same time.


- Another alternative is to use a power switch which is plugged into both rails. Outputs from this power switch would then be used to supply power to all four switches.



Leo Laohoo Tue, 03/17/2009 - 15:30

Talking about power ... Don't go and use those cheapie power boards you find in your local supermarket/pharmacy.


I'd look for the following:

- Metal enclosure;

- 1RU/2RU, rack-mount capable;

- Long power cord (3-5 metres); and

- 15amp capture plug

vincent-n Tue, 03/17/2009 - 15:34

I just look up some information on the 2300 RPS http://www.cisco.com/en/US/docs/switches/power_supplies/rps2300/hardware/installation/guide/rpsinst.html


Found this interesting reading in the document

"The switch connected to the RPS 2300 might restart when it changes from RPS power to its internal power. We recommend that you first divert switch traffic to an alternate switch to avoid data loss. This does not occur on the Catalyst 3750-E or Catalyst 3560-E switches."


What is the point of using the RPS unless you have the -E series switches?

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