Understanding Performance Numbers and Sizing a Router

Answered Question
Jul 5th, 2010

Hi, I am trying to understand the performance numbers in the routerperformance.pdf sheet located at

http://www.cisco.com/web/partners/downloads/765/tools/quickreference/routerperformance.pdf

If the requirement is to size a router for a location which will have 100Mb WAN Ethernet Link and 50 - 100 Users what would be the device/s that can provide maximum benefit as well as scaling for future growth should the WAN link be upgraded to 200Mb or even 1Gb in the future.

I was looking at the ISR3845 and it says that the device is capable of 500Kpps and 256Mbps based on 64byte frames. How do these numbers relate to each other as from what I have been reading it seems that for a 1Gb link the minimum number of 64byte frames required is 1,488,096 wheras in this pdf it says that the 3845 can only do 500Kpps. Does this mean that the ISR3845 cannot do 1Gb.If it cannot than what is the point of having 2 onboard 1Gb interfaces as well providing 4 x HWIC's that can also be 1Gb. Do the numbers relate to the entire performance of the router or the HWIC's will provide their own performance separate from what is offered as standard?

For the requirement above if the switch is a 3750 stackable and it uplinks to the 3845 with a  2x 1Gb bundled L3 point-to-point link than would it be able to handle the load if the traffic on that uplink is at a constant rate of 500 - 700Mb during peak times and if the WAN link itself was 1Gb. How does one evaluate if a router can or cannot handle this and what are some other considerations in making such decisions? Tx

I have this problem too.
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Correct Answer by Edison Ortiz about 6 years 5 months ago

Does this mean that the ISR3845 cannot do 1Gb.

Correct.

If it cannot than what is the point of having 2 onboard 1Gb interfaces as well providing 4 x HWIC's that can also be 1Gb. Do the numbers relate to the entire performance of the router or the HWIC's will provide their own performance separate from what is offered as standard?

Access port to a Gigabit network but unable to provide line rate speeds. You will find similar issues with modular switches were access ports can be 1Gbps or 10Gbps but throughput will be a lot lower. It's always recommended to read the data sheet on any product.

For the requirement above if the switch is a 3750 stackable and it uplinks to the 3845 with a  2x 1Gb bundled L3 point-to-point link than would it be able to handle the load if the traffic on that uplink is at a constant rate of 500 - 700Mb during peak times and if the WAN link itself was 1Gb. How does one evaluate if a router can or cannot handle this and what are some other considerations in making such decisions? Tx

The router will be running under constant high CPU because it will be unable to handle the load. For such requirement, you need to look into the switch line instead of the router line, unless you are planning to move up to the 7200 VXR line.

Regards,

Edison

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Correct Answer
Edison Ortiz Mon, 07/05/2010 - 12:52

Does this mean that the ISR3845 cannot do 1Gb.

Correct.

If it cannot than what is the point of having 2 onboard 1Gb interfaces as well providing 4 x HWIC's that can also be 1Gb. Do the numbers relate to the entire performance of the router or the HWIC's will provide their own performance separate from what is offered as standard?

Access port to a Gigabit network but unable to provide line rate speeds. You will find similar issues with modular switches were access ports can be 1Gbps or 10Gbps but throughput will be a lot lower. It's always recommended to read the data sheet on any product.

For the requirement above if the switch is a 3750 stackable and it uplinks to the 3845 with a  2x 1Gb bundled L3 point-to-point link than would it be able to handle the load if the traffic on that uplink is at a constant rate of 500 - 700Mb during peak times and if the WAN link itself was 1Gb. How does one evaluate if a router can or cannot handle this and what are some other considerations in making such decisions? Tx

The router will be running under constant high CPU because it will be unable to handle the load. For such requirement, you need to look into the switch line instead of the router line, unless you are planning to move up to the 7200 VXR line.

Regards,

Edison

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