Are 3560 Wire Speed?

Unanswered Question
Aug 2nd, 2007

It says 32 Gbps, does that mean its wire speed for 24 port switches?

I have this problem too.
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wochanda Thu, 08/02/2007 - 18:54

The 32Gbps is a limitation on the bus between the asics controlling the ports. It is unidirectional, so it can only handle 16 full-duplex gig streams.

Since standard 3560's have 24/48 FE ports with 2-4 GE ports, they are line rate.

Only the 3560G's have potential limitations on how much you can send on the backplane.

The successor to the 3560, the 3560E, comes standard with 24/48 GigE ports and 2 10GigE ports, and has no such limitation on the backplane, so it will do wire rate.

cisconoobie Fri, 08/03/2007 - 06:47

I just want to understand it a little better.

So if I am using a 3560G and have 20 servers connected to it. If all 20 servers start transfering data between eachother at the same time, I will only get a max of 16 Gbps of bandwidth on the backplane?

If we count:

1. Each server sending files = 16 Gbps

2. Each server receiving files = 16 Gbps

Total comes out to 32 Gbps, am i correct here?

What happens to the missing 4 Gbps? In this case of 20 servers, would it be 1.25:1 oversubscription ?

Please clarify for me, also would you know what port groups are controlled by each asic?

wochanda Fri, 08/03/2007 - 10:37

On a 3560G each group of 4 ports is on a single ASIC. Therefore the amount of inter-asic traffic needs to be kept at 32Gb half duplex.

Your math is more or less correct. If packets aren't able to fit on the ring, you'll see overruns and input drops on your interfaces.

wochanda Mon, 08/06/2007 - 07:01

No, the E switches have a built in switch fabric, so they are fully non-blocking.

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