Metro Ethernet Switch vs 3845 Router

Unanswered Question

My company has a site where we have debated the difference between installing a T3 vs 50Mb Ethernet.

We typically deploy 3845's in this scenario. T3 prices (monthly cost & hardware costs) are not cheap and ethernet (especially with inexpensive hardware) looks promising.

We would need to use shaping on the interface to their upstream PE device, so which platform is better for this? ISR series or Metro Switches?

I understand that the ISR would be queuing in software vs the switch's hardware. How hard would that hit the 3845 or any of the ISR's for that matter?

Any links or advice would be appreciated. We would definitely like to move to ethernet in the future over other technologies (ATM, T1, T3, Frame, etc).

I have this problem too.
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Paolo Bevilacqua Mon, 09/28/2009 - 13:03

In your case, what's the price difference?

You will find that is usually a winning argument and with reason.

Joseph W. Doherty Mon, 09/28/2009 - 15:42

The biggest pluses to a L3 Switch cost and performance. The biggest minus, not as feature rich. The Metro Ethernet switches do provide some additional features to help narrow the gap between switches and routers.

I've done a bit of QoS queuing on various ISRs and 7200s. There is a performance hit, but I haven't found it a problem when router properly sized for expected load. (I recall[?] "book" might call for an additional 10 to 20% load.)

PS:

BTW, if you need to shape for Ethernet, don't forget (at least on routers), shaping might only account for L3 when you also need to account for L2.

Now I think I understand the difference. The switch will shape down to Layer2...whereas the router will shape on L3 only.

Thanks for the reply. This is so confusing, because it seems like all the devices (even regular switches) shape with SRR commands. This is not explained very well anywhere. If anyone has any links or documentation they would like to share, i'm all ears.

csco11142276 Wed, 09/30/2009 - 11:27

I reckon in your case 3845 will do the far better job. I hope you wont have any scalability plans above 50 Mbps, but even if you scale with another 50Mbps still 3845 is good to go, ISR 3845 is a beast.

If you are still worried then use one HWIC slot with HWIC-1GE-SFP (rate limit down to 50Mbps). The HWIC bus interface is limited to 400 Mbps of full duplex. The actual throughput of the Gigabit Ethernet HWIC is limited by the throughput of individual platforms. Under bidirectional traffic of 1518 bytes or larger, the Gigabit Ethernet HWIC can support up to an aggregate of 500Mbps on 3800 platforms which is far higher than what your requirement is.

Also remember, your ISP may provide their NTU in front of ur router. In cases like 50Mbps to 100Mbps the NTU they supply is much smaller than 3845 router. You would just laugh looking at it if you compare with 3845, but it does QoS, security and Q in Q all no bother.

If this any helps, please rate it.

Danilo Dy Wed, 10/07/2009 - 08:37

Ethernet (or MetroE) is cheaper compare to other old technology (with a detoriorating infra) and it can scale to higher bandwidth.

If the connection is private wan, I recommend Metro Switches over ISR not only because of cost but also QoS. If you can avoid rate-limiting don't do it, as it does something bad to the TCP packet.

Dandy

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