How impact the policy-map to the CPU utilization?

[cjrchoi11]

I'm simulating the traffic in the 2821 router with packet generator.

-284 bytes packet, 47Mbps with QoS getting 100% CPU

-284 bytes packet, 47Mbps without QoS getting 50% CPU

-1416 bytes packet, 200Mbps with QoS getting 80% CPU

-1416 bytes packet, 200Mbps without QoS getting 30% CPU

I found the policy-map makes big impacts the CPU utilization. especially in the case of small packet. actually, I experienced in the production environment by the virus packet with the same result.

47Mbps(284bytes, 22Kpps) is kind of small amount of traffic versus the giga interface but it make clash the router when the policy-map configured.

Is there any information how the policy-map impact the CPU utilization or design tips?

Thanks,

[pkhatri]

Hmm.. I'm curious. Is this a 2821 we are talking about ? The maximum rated throughput for the 2821 is 87Mbps. How did you managed to get 200Mbps ? How are you counting this ?

Paresh

[cjrchoi11]

its by traffic generator and don't know the actual 2821 interface bandwidth at the moment. anyway, my point is how impact the CPU by the policy-map. especially the small packet size. I just want to get a general idea.

Thanks,

[pkhatri]

In general, routers are rated based on the packet forwarding performance as packets per second (pps). Therefore, a router that does 20000 pps will do 20000 pps for pretty much any size of packet. However, running 20000pps of 100-byte packets will result in lower Mbps throughput than doing the same for 1500-byte packet.

The point I am trying to make is that if you are passing X Mbps of traffic through a router with say, 100-byte packets compared to the same X Mbps with 1500-byte packets, the resulting pps will be much less for the 1500-byte packets at X than it will be for the 100-byte packets at X.

The bottom line is that the router is going to be taxed harder with smaller packets (assuming the rate of traffic is the same) and your CPU will rapidly ramp up.

Hope that helps - pls rate the post if it does.

Paresh

[Georg Pauwen]

Hello,

regarding the policy-routing and the CPU utilization, I noticed the same thing, the CPU utilization shoots up. The reason for that is that apparently the traffic handled by the route map is being process-switched. Cisco recommends enabling ´ip route-cache policy´ on the interface where the route map is applied to...

Regards,

GP

[pkhatri]

Hi Georg,

The 'ip route-cache policy' command only applies when doing policy-based routing. The original poster is more interested in enabling QoS using policy-maps, a different concept...

Hope that helps,

Paresh