Paolo Bevilacqua Mon, 02/04/2008 - 03:45

If true 100 mbps, will not quite suffice when enough traffic is offered. See attached document.

Note quite often ISPs promise the moon and sky, then deliver a light bulb!

Hope this helps, please rate post if it does!

saimbt Mon, 02/04/2008 - 03:50

i know how the isp's act. i only want to provision a router that can 100 mbps as a worst case ;)


Goutam Sanyal Mon, 02/04/2008 - 04:04


It will work normaly, if you handel the router properly, I mean QOS, CEF etc. etc.



Paolo Bevilacqua Mon, 02/04/2008 - 04:38


not sure if you have read the document that I've sent before. Maximum throughput of a 3825 is 180 mbps for 512 bytes packets and ideal conditions.

That is a bit less of a fast ethernet fully loaded on both directions.

Goutam Sanyal Mon, 02/04/2008 - 04:48


Do u think, with that condition it will not work properly?

A Cisco 3825 Router has 2GE port, which is sufficent to carry 100 MBPS MEN.

If not, pls shed light on.



Paolo Bevilacqua Mon, 02/04/2008 - 05:12

Hi, traditional routers are based on a CPU, just like computers. The more packets the router receives, the more load for the CPU.

Once the maximum processing power is reached, the CPU load is 100%, the router will drop packets and will be slow in responding. In short, there will be big problems.

No matter the number or speed of the installed ports, a 3825 router cannot handle more than 350,000 packet per second, that equates to 180 mbps of traffic using 512 bytes packets.

Hope this helps you understand a bit more.

Joseph W. Doherty Mon, 02/04/2008 - 17:57

From the performance chart Paolo provided, we see the 3825 is rated at 350 Kpps and 179.2 Mbps. At the top of the document, it notes "Mbps calculated by pps * 64bytes * 8bits/byte", and, indeed, 350,000 pps * 64 bytes * 8 bits = 179,200,000 bps. Also noted, this is without any services and perhaps using them ". . . performance will decline significantly from the given numbers . . .".

What may not be clear, if you increase the packet size, effective performance improves. For instance, if the packets were 1518 bytes (non-jumbo Ethernet maximum), we get 350,000 pps * 1518 bytes * 8 bits = 4,250,400,000 bps (about 4 gig). Disregarding impact of services, worst case bandwidth might be as low as 179 Mbps but best performance could be as high as 4 Gbps.

You average performance will depend on your average packet size, so assume yours run about 128 bytes (possibly smaller than one would expect, but good to be pessimistic), you should see an average performance of 350,000 pps * 128 bytes * 8 bits = 358,400,000 bps, 358 Mbps.

Before you jump for joy and think the 3825 can easily handle 100 Mbps, first also know the above is for an unidirectional flow. Assuming you want to do 100 Mbps in both directions, the above numbers are halved. Second, don't forget the you many encounter ". . . performance will decline significantly from the given numbers . . .".

Bottom line,

"I have a requirement for 100 Mbps MEN.

Will a Cisco 3825 suffice this requirement?"

perhaps, perhaps not. Much will depend on your actual traffic packet size mix and what IOS features you configure.

If you already have a 3825, you could try it, but monitor the CPU utilization, which as Paolo also noted, is what's likely to be the resource limiter.

Danilo Dy Mon, 02/04/2008 - 18:38


From what Paolo and Joseph have provided ,you should be able to see the big picture and decide which is appropriate for your current and future need.

As what Joseph mentioned, if you already have the 3825, you can try it, if possible avoid running other services and feature (IPSec VPN).

If you don't have the 3825 yet, since you already need 100Mbps now, there's a chance that you need to upgrade this link in the future (future growth). If budget is not a constraint You can look into 7200-NPE-G1 (500Mbps) 7200-NPE-G2 (1Gbps) which is the ideal Internet router for high bandwidth.



saimbt Mon, 02/04/2008 - 21:20

Thank you all for the knowledge sharing... I am really impressed..




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