High cpu on router during intensive traffic

[a.dardare]

Could anyone have an idea about what sort of configuration I can set to optimize the cpu utilization on a router?

I have already activated the CEF on each interface, in vain!

My router is 2651XM with a processor running at 80Mhz and 128Mb of RAM. The IOs is the 12.3(8)T1. All interfaces are set to 100Mb Full duplex.

When a windows server connected to one interface sends a big file (2Gb for example) to a windows pc connected to the other interface, the router CPU goes up to 60%. There are no access-lists configured on the router. And there is no throttles, no errors ...

I thank you very much in advance for your help.

[BertimusMaximus]

Try using the show proc cpu command when the cpu utilization is high. Check to see what process is causing the spike.

[a.dardare]

Hi BertimusMaximus,

Thank you very much for your answer. But I allways perform this command and still can't see any process that use high cpu. The output for this command is something like :

"CPU utilization for five seconds:62%/60% ..."

So you don't need to search for a process since all processes use only 2% of CPU in this example.

Is there anything special you have to configure when dealing with forwarding traffic between Windows pc using SMB protocol?

Thank you.

[tekha]

You say "All interfaces are set to 100Mb Full duplex", does that meen that you are routing between two FastEthernets running 100Mbps, because according to this http://www.cisco.com/warp/public/765/tools/quickreference/routerperformance.pdf the 2650XM will only forward 40,000 pps with CEF, and that migth not be 100Mbps.

So the router is probably doing its best.

Just because you can have two FastEthernet in the router, doesn't meen it will forward 100Mbps, a 2800 router would do it however.

[a.dardare]

Hi tekha,

I totally agree with you and I am aware of these characteristics but every time I was checking the interface statistics, I never got more than 8000pps. And since there is 0 throttle from the interface, I assume that there is no hardware limitations from the router.

Have you read my question related to any special configuration when forwarding gigabit trafic between windows servers using SMB through a router?

Best regards,

Annick Dardare.

[dino.demarco]

The 40,000pps throughput is based on a packet size of 64bytes. However, your client/server communication is more likely to use a higher average packet size. This will translate to a lower pps througput. For example, the 8,000pps you mentioned with an average packet size of 320bytes would equate to 40,000pps with 64byte packets.

Tekha is correct. Your router is doing all it can and based on the info provided there is no confiuration that can improve the performance you are seeing. In fact, I encountered a similar problem (but with different hardware; a 2621) and the only solution was a hardware upgrade.

[a.dardare]

Hi Dino,

I would like to thank you very much for your help. And I also apologize to tekha because I didn't read tightly what was written in the documentation he had forwardee to me.

I have sniffed the network and I got the size of the IP packet the windows servers use and it's 1500 bytes and during the test my router use up to 90% of CPU and the amount of packet transmitted is 1200 pps instead of 1700pps for a 1500bytes IP packet size.

Thank you and best regards,

Annick.

[ceri]

Are you sure about that, I am experiencing the exact same problem, but my router (2621XM) has a throughput of 30k pps, so using your calculation if it does indeed actually include size too then the max bandwidth of my router is 64 x 30000 = 1875KB/s. Suerly that cant be correct, that's only just over 10Mbit ethernet

[ceri]

I have actually double checked this with cisco now. And it is not true.

The quoted pps throughput is independant of frame size, simply because the data is not copied. It's the number of routing decisions etc... that the router can cope with a second. So theoretically (using the 100Mbit ethernet max frame size) you should be able to get 1500 * 30000 = 44MB/s which far exceeds the bandwidth for 2 FastEthernet controllers