Cisco Catalyst 2948G-GE-TX - use SFP uplinks?

Unanswered Question
May 19th, 2007

I wanted to get an independent opinion...

I have inherited a wiring closet for an office with four Cisco Catalyst 2948G-GE-TX switches handling all the patches from the user office ports.

This model supports 1000BASE-T on all 48 ports, and has four SFP ports (currently empty of transceivers.) I am about to re-wire the entire closet, as it is a spaghetti monster.

So I have a PIX, two routers, and the four switches in there. Right now, the wiring is all Cat5/Cat5e, and no SFP ports are in use. Is there any advantage to using the SFP ports to connect my switches together?

Normally, the primary advantage would be the Gig-E speed, but all 48 ports have 1000BASE-T. (Also, the SFP ports allow links to be hundreds or thousands of meters away - but I'm all in the same rack, so copper is fine.)

I'm unsure whether the Cisco switches would perform better using the SFP ports because of optimization in administrative overhead between the switches, whether some sort of trunking should be configured, etc.

Also, if using the SFP ports IS recommended, what's the best configuration - a master switch with three branches to the others? And given a tree like that, is there benfit to also cross-linking the branches for machine-to-machine communications?

I wouldn't mind cross-linking all four switches together if there's a speed benefit, but I doubt it would be much - if any - and looking at 4 x 4 = 16 transceivers at $300 a pop starts to add up.

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adavenport Tue, 05/22/2007 - 19:40

There would be no particular performance increase by using the sfp slots. I'd just use copper. If the switches don't do auto MDIX, then of course you need crossover cables.

As to in-line or tree, it might depend on whether you also have any high performance servers on the network, where you want to minimize latency to any client.

Cross-linking would require spanning tree to break loops, so no particular advantage other than failover should an interconnect fail. You can do that with copper, too, if you like.

HTH, Roger


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