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High CPU on 3750 running routing

Hi,

I have a small network of 4 x 3750s running routing (OSPF) which contain all company firewalls. It bridges internal trusted corporate networks (depots etc) to external untrusted networks (Internet/Datacenter networks). It sees a fairly high level of traffic running through it (it gets forwarded to firewalls at gig speed).

OSPF is costed to remove asymetric routing so one 3750 is acting as primary and does most of the work. The 3750s are in area 0, and all other areas are summarised to some degree. However, CPU is running high on the 3750 when looking at the history at times:

PPFX_X37_274#sh ip ro summ

IP routing table name is Default-IP-Routing-Table(0)

IP routing table maximum-paths is 32

Route Source    Networks    Subnets     Overhead    Memory (bytes)

connected       0           3           192         456

static          53          549         90816       91504

ospf 1          13          1945        128768      297616

  Intra-area: 67 Inter-area: 903 External-1: 983 External-2: 5

  NSSA External-1: 0 NSSA External-2: 0

internal        22                                  25784

Total           88          2497        219776      415360

PPFX_X37_274#sh proc cpu | exc 0.00

CPU utilization for five  seconds: 26%/18%; one minute: 26%; five minutes: 26%

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

   4    93091018   6079803      15311  0.95%  0.18%  0.14%   0 Check heaps

129    16401387  75768455        216  0.15%  0.04%  0.03%   0 HL3U bkgrd proce

184    81753329 515763429        158  0.47%  0.19%  0.16%   0 IP Input

290    66535786  35750699       1861  0.47%  0.24%  0.17%   0 SNMP ENGINE

100                        *                   *

90         *             **                   *

80         *             ** *                 *                     *  *

70 *       *           * ** *               * **                    *  *

60 *  **   *     *     * ** *   *   *       * ***     *    *   * *  *  *

50 *****   *  ** ** * ** **** ***   *   * * * ****    * *  *  ***** *  **

40 ******************************  **********************  ** ******* ***

30 ###*****************#*####*****************#**************************

20 #######*#############################################################

10####################################################################

   0....5....1....1....2....2....3....3....4....4....5....5....6....6....7.

             0    5    0    5    0    5    0    5    0    5    0    5    0

                   CPU% per hour (last 72 hours)

                  * = maximum CPU%   # = average CPU%

My question is - although the average is around 26% the 72hour picture would suggest that CPU is running at 100% at times. Is this an imminent concern that needs re-designing, or is this normal behaviour (SPF running for instance) that is manageable?

thanks

Phil

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1 REPLY
Cisco Employee

High CPU on 3750 running routing

Hello Phil,

Can you also have a look at show processes cpu sorted ? Try out also 1min and 5min keywords to see what processes tend to create a long-standing load on your CPU. This command should place the most CPU-intensive tasks at the top of the listing so you can see what process is consuming most of your CPU time.

Having a load in the range of 26% is, in my personal opinion, nothing to be especially concerned about, but I do not quite like the spikes up to 100%. They need more investigation indeed.

This may look like trying to solve your issue quickly but I really recommend going through the following documents:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/troubleshooting/cpu_util.html

http://www.cisco.com/en/US/products/hw/switches/ps5023/products_tech_note09186a00807213f5.shtml

They describe some of the most common causes very nicely. Please do inform us about any issues you will find out!

Best regards,

Peter

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