Cisco router CPU utilisation question

[Parves Ataev]

Hi folks,

I am trying to understand cpu utilisation on Cisco router. I have Cisco 2921 router which is forwarding about 200Mbit/s of traffic IP CEF+NAT. Several subinterfaces with real IP address and several subinterfaces with private Ip address (NAT). Router runs OSPF. Nothing fancy just routing really. The average CPU utilisation is about 40%, BUT when I view the detailed output of what process is using CPU I dont understand why I am not seeing what i want to see. In other words i see the utilisation of 39% in the below output but sorting out the output by excluding processes that are idle (0.00%) doesn not show the exact processes which are utilising 39% of CPU. Are there hidden proccesses that are are not shown? Can someon explain me please. Many Thanks

Router#show processes cpu | ex  0.00%  0.00%  0.00%

CPU utilization for five seconds: 39%/39%; one minute: 39%; five minutes: 39%

PID Runtime(ms)     Invoked      uSecs   5Sec   1Min   5Min TTY Process

   2       24000     4586020          5  0.00%  0.01%  0.00%   0 Load Meter

   3        2512        1886       1331  0.00%  0.06%  0.01% 388 SSH Process

   6    23615872     3322276       7108  0.00%  0.05%  0.05%   0 Check heaps

  13    18559636      381860      48603  0.00%  0.04%  0.05%   0 Licensing Auto U

  14    21932740    22905991        957  0.00%  0.04%  0.05%   0 Environmental mo

  31     7608500    90733108         83  0.07%  0.03%  0.02%   0 ARP Input

  52       15512    22906045          0  0.07%  0.00%  0.00%   0 TTY Background

  65      301052    22938414         13  0.07%  0.04%  0.05%   0 Per-Second Jobs

  83      179528    91709616          1  0.07%  0.11%  0.10%   0 Netclock Backgro

  95     2747668    45851656         59  0.00%  0.02%  0.01%   0 BPSM stat Proces

  98       81596  2908301799          0  0.15%  0.15%  0.15%   0 Ethernet Msec Ti

123       38804   715304987          0  0.00%  0.03%  0.02%   0 IPAM Manager

127    27535868   218837999        125  0.07%  0.07%  0.07%   0 IP Input

146      247004    32897319          7  0.00%  0.02%  0.00%   0 CEF: IPv4 proces

268     5334052    35133146        151  0.15%  0.02%  0.00%   0 OSPF-1 Router

269    16417748   179951516         91  0.07%  0.04%  0.05%   0 OSPF-1 Hello

[ravikantt]

Hi Parves,

Your 'Sh processes" output shows that "39%/39%" means this CPU utilization not because of any control processes, but because of data forwarding, your router's CPU is busy in data  forwarding, not in control processes like, OSPF etc.

You must check if the "CEF" is enabled on router (although default CEF is on); or whether any interface(s) has "no ip route-cache" command configured on.

Router#show processes cpu | ex  0.00%  0.00%  0.00%

CPU utilization for five seconds: 39%/39%; one minute: 39%; five minutes: 39%

PID Runtime(ms)     Invoked      uSecs   5Sec   1Min   5Min TTY Process

   2       24000     4586020          5  0.00%  0.01%  0.00%   0 Load Meter

   3        2512        1886       1331  0.00%  0.06%  0.01% 388 SSH Process

   6    23615872     3322276       7108  0.00%  0.05%  0.05%   0 Check heaps

Below is the link for your understanding & clarification.

http://www.cisco.com/en/US/products/sw/iosswrel/ps1828/products_tech_note09186a00800a65d0.shtml

Cheers

Ashok

[comsameer]

1. Check CEF, should be enabled on router, also check how packets are switching using "show interfaces switching" command.

2. Check Broadcast in LAN High cpu utilization is usually due high broadcast traffic that hits the device

3. Disable "virtual-reassembly".

4. Try upgrading IOS.

[Joseph W. Doherty]

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Posting

As also noted by Ashok, your "hidden" CPU is "interrupt" CPU, which is fast path packet forwarding.  For a 2921, 40% for about 200 Mbps sounds about right.  Cisco only recommends the 2921 for up to 50 Mbps of WAN bandwidth.

[medhat elsaeed]

- the 39% means the interrupt processing which represents the data forwarding not the control plane processes.

And because this router is Processing Based ( which means that the data forwarding and control plane functions are being handle by the processor) as there is no dedicated HW for the forwarding like the High End routers ( CRS, ASR) , So the traffic forwarding will take a portion from the CPU.

Check the below output from a 7200 router:

Load for five secs: 24%/20%; one minute: 22%; five minutes: 20%

Time source is NTP, 11:06:58.864 CLT Mon Jun 3 2013

CPU utilization for five seconds: 24%/20%; one minute: 22%; five minutes: 20%

The 24% represents the overall CPU utilization

The 20 % represents the CPU utilization of traffic forwarding

.