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Cisco 2811 High CPU usage

We've got a Cisco 2811 that experiences periods of extremely high cpu usage.  It looks like the problem is CPU inturrupts.

When I run "sho proc cpu sort" it shows the cpu at 98%/84% for instance this morning.  However the list of processes total up to less then 25%.  Taking a look at the cpu history I can see that sometimes the high cpu usage last for 20-30minutes and sometimes its just a blip for a few minutes.  Either way DNS lookups from our web filter take forever and web browsing slows way down.

We have a 10mb WAN link, 100Mb internal link. I can't seem to pin down what exactly is happening but we do some offsite backups (lots of udp traffic) as well as sql replication to a link across town.  My guess is that while these backups are running we may be hitting the packet per second limit of the router.  I'm also seeing throttles and drops on the interface.

If I take a look at "show interfaces switching" I see the following statistics:

FastEthernet0/0 Internet/WAN
          Throttle count       5267
                   Drops         RP       7514         SP          0
             SPD Flushes       Fast          0        SSE          0
             SPD Aggress       Fast          0
            SPD Priority     Inputs   40761680      Drops          0

    Protocol  IP
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                 Process  127322510 2383955614 2352954007 3315779514
            Cache misses          0          -          -          -
                    Fast  271993481 2730636105 1515972958 2966490960
               Auton/SSE          0          0          0          0

    Protocol  DEC MOP
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                 Process          0          0      34883    2685991
            Cache misses          0          -          -          -
                    Fast          0          0          0          0
               Auton/SSE          0          0          0          0

    Protocol  ARP
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                 Process     946716   56802960     855642   51338520
            Cache misses          0          -          -          -
                    Fast          0          0          0          0
               Auton/SSE          0          0          0          0

    Protocol  Other
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                 Process     349632  127615230    2097138  125828280
            Cache misses          0          -          -          -
                    Fast          0          0          0          0
               Auton/SSE          0          0          0          0

    NOTE: all counts are cumulative and reset only after a reload.

IP inspect is on and we do have a couple of gre tunnels setup on the router also.

Time to upgrade???

2 REPLIES 2
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Cisco Employee

Re: Cisco 2811 High CPU usage

84% CPU is due to interrupts..

Please follow the procedure mentioned in the link to tshoot high cpu due to interrupts.

http://www.cisco.com/en/US/products/hw/routers/ps359/products_tech_note09186a00801c2af0.shtml

Karthic.R.S

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Hall of Fame Mentor

Re: Cisco 2811 High CPU usage

Erik,

The 2811 should be able to support 10Mbps WAN connection. I noticed you have a FastEthernet connected to the 10Mbps WAN.

Did you change the speed to 10 on the interface? If not, the router will try to send at 100Mbps which may cause packet drop and retransmission.

You have 2 options, either set the speed to 10Mbps manually or implement Hierarchical QoS with a parent policy shaping at a value lower than 10Mbps.

Regards,

Edison

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