High CPU utilization on 7201

Unanswered Question
Mar 26th, 2009

Hello friends,

I had 7206-NPE-G1 for routing purposes and PBR, IP CEF is on, no ACL, no dynamic routing just static.

Well 1 gbps in and 1 gbps out. That is all. CPU was about 82% as highest.

After that decided to replace 7206-NPE-G1 with 7201 (G2) as it should be TWICE as stronger.

But nothing of the kind!!!

We have the same 82% as highest, not 41% as was expected.

I promised to my boss to lower CPU load at least 1,5 times...


Eugene Melnikov

I have this problem too.
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Giuseppe Larosa Thu, 03/26/2009 - 02:41

Hello Eugene,

when I did tests on NPE-G1 I've found values in agreement with your tests or worse with full duplex traffic.

note that C7200 is declared to have the following processor:


1.67-GHz Motorola Freescale 7448 processor


2,000,000 pps or more


here it is NPE-G2


note that with small packets you need almost 1,400,000 pps to fill a single GE in one direction

So a C7200 is good to handle 500 Mbps full duplex

Hope to help


a.alekseev Thu, 03/26/2009 - 03:18

could you show the output?

sh run

sh int g0/0

sh int g0/1

sh proc cpu sort 5min

Joseph W. Doherty Thu, 03/26/2009 - 05:24

Just wondering whether traffic bandwidth utilization didn't increase at all. With such high CPU utilizations, it's possible packet forwarding might be held back by insufficient CPU. Faster CPU could peak at same utilization percentage, but might have increased bandwidth utilization.

In other words, your expectation for a decrease in the G2's CPU might only be true if offered load to the G1 was well within its capacity. If not, a faster CPU should do more, but the utilization might not drop.

When you note 1 Gbps in and out, that much actual traffic can max out either a G1 or G2, I believe. For minimum sized packets, doing only the minimum processing just to forward packets, the two engines can, in theory, forward a maximum of 500 Mbps or 1 Gbps, respectively (and you note you're pushing 2 Gbps). As packet size increases, bandwidth usually does to, a 2 to 4x increase isn't uncommon, and if true (for you), you're still might be borderline with a G2.

Normally I recommend a software router with 4x (or 2x minimum) the expected traffic load. For true gig (duplex), that would be a router with about 8 to 12 Mpps capacity, currently that would place you into the ASRs. (If wondering, but 7200s have gig interfaces, they do, but so do 2821s, which I wouldn't expect to sustain full gig duplex load.)

I also recall reading somewhere that Cisco software based routers don't work at their best when running so busy. Something about they work better when there's some reserve CPU capacity to handle their various software processes.

One of the things Aleksey asked for was a show process CPU. Of immediate interest is whether most of your CPU is servicing "interrupt". If it is, generally this would indicate you router just isn't powerful enough (still) for the offered load. If there's a large percentage of non-interrupt processing, it may be possible to decrease that.


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