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to stack or not to stack

A design question.

If i have two core/distri switches, and 7 access switches, should i stack these access switches and connect the first one to core 1, and the last stack switch to core 2, or should i connect every switch to both core switches.

What are the rules for this, if any? Both solutions are redundant.

3 REPLIES

Re: to stack or not to stack

Check this link for the 2 types of stacking you can do, Daisy chain or Star configuration (for which you ll need an additional switch with just GBICs).

http://www.cisco.com/warp/public/cc/pd/si/casi/ca3500xl/prodlit/c3524_ds.htm

Performance wise, Star configuration is more efficient, than the Daisy chain configuration.

You can save on gbics and fiber, if you connect it the first way, that is connect the end switches to core 1 and core 2, while stack all the switches together in a daisy chain configuration. This solution is also redundant.

A star configuration (of connecting each switch to core), provides a good redundant design, but at the cost of more gbics and fiber.

New Member

Re: to stack or not to stack

Thanks for your answer.

I am aware of the stacking methods, i've used them all in the past.

I was just looking for a technical point of view. Spanning -tree, Qos, what is better in this particulair case...

Re: to stack or not to stack

Hi,

from bandwith and Spanning Tree point of view:

1) If you daisy chain the access switches using both ports on each GigaStack GBIC you degrade the speed to 1Gbps half-duplex "bus" connecting all switches in the stack. It's an equivalent to connecting them all to one 1Gbps repeater.

2) If you connect each access switch to the core you have 1Gbps full-duplex line to each switch. But for redundancy it's better to use two uplinks on each access switch. But it would require 28x 1000Base-SX GBICs for 7 access switches - pretty expensive.

3) You can daisy-chain access switches using two GigaStack GBICs in each access switch. This will leave full-duplex connection between all switches. But the STP network diameter will be large.

4) I'm using a combined topology in my network:

Each pair of access switches (let's call them AS1, AS2) is connected together via GigaStack GBICs (full-duplex). AS1 is connected to one core switch, AS2 to the other core switch via 1000Base-SX GBIC. (Sometimes it's necessary to tune STP port costs to ensure the traffic use only uplinks under normal conditions but it's not so complicated.)

This approach gives me full-duplex bandwith, full redundancy and a small network diameter in a reasonable price.

HTH,

Milan

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