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How to resolve high CPU utilization on routers

Core Issue

These are common symptoms of high CPU utilization:

  • High percentages in the output of the show processes cpu command

    If you have the show processes cpu command output or a show tech-support command from enable mode, display potential issues and fixes from your Cisco device by referring to the Output Interpreter tool.

  • Input queue drops
  • Slow performance
  • Services on the router fail to respond, for instance: 
    • Slow response in Telnet or unable to Telnet to the router.
    • Slow or no response to the ping command.
    • The router does not send routing updates.
  • If the router is being overloaded with traffic or the traffic not taking the optimal switching path through the router, the issue can also be caused by the Blaster and Nachi worms.

  •    You can see what are the processes shooting your CPU utilization using following command:

Router#sh processes cpu | exclude 0.00%__0.00%__0.00%

CPU utilization for five seconds: 2%/100%; one minute: 1%; five minutes: 1%

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

   2           8     13918         0 0.00% 0.02% 0.00%   0 Load Meter

   5       66924     8516       7858 0.65% 0.10% 0.06%   0 Check heaps

20       10148     19914       509 0.00% 0.02% 0.00%   0 HC Counter Timer

30       3980     25100        158 0.00% 0.01% 0.00%   0 Net Background

33       1768     69568         25 0.00% 0.01% 0.00%   0 TTY Background

34       3912     69584         56 0.00% 0.02% 0.00%   0 Per-Second Jobs

64       12556   2172687         5 0.24% 0.21% 0.19%   0 ACCT Periodic Pr

68       12240   2172686         5 0.16% 0.17% 0.18%   0 IP ARP Retry Age

78       1088   271810         4 0.08% 0.02% 0.00%   0 SSS Feature Time

92       16732     86322       193 0.00% 0.06% 0.04%   0 CEF process

108       6856     69572         98 0.00% 0.01% 0.00%   0 RUDPV1 Main Proc

110       2364     69574         33 0.00% 0.01% 0.00%   0 bsm_xmt_proc

114       12892     1161     11104 0.00% 0.01% 0.00%   0 Adj Manager

127       5600   695694         8 0.08% 0.10% 0.09%   0 RBSCP Background

130       5392       854       6313 0.98% 0.30% 0.12%   0 Exec

220       46188     13920       3318 0.00% 0.05% 0.07%   0 Compute load avg

  • You can also check your CPU history in graphical pattern using "show processes cpu history"  command to see High CPU spike.

Router#show processes cpu history

Router   07:25:36 PM Friday Mar 1 2002 UTC

   2222233333                         1111111111

100

90

80

70

60

50

40

30

20

10

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

             0   5   0   5   0   5   0   5   0   5   0

               CPU% per second (last 60 seconds)

   11111221113111111111111111112121111111111 221111111111111111

100

90

80

70

60

50

40

30

20

10

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

             0   5   0   5   0   5   0   5   0   5   0

               CPU% per minute (last 60 minutes)

             * = maximum CPU%   # = average CPU%

     4           11

   2322333222232223425

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%

Router#

Resolution

To resolve this issue, determine the accessibility of the router by performing these steps:

  1. Determine if you are able to issue the show commands on the router. If so, start collecting more information immediately using these show commands.
  2. Determine if the router is inaccessible and if this problem is reproducible. If so, power-cycle the router. Before reproducing the problem, configure the scheduler interval 500 command; this schedules low priority processes to run every 500 ms. This provides time for you to run some commands, even if CPU usage is at 100 percent. On Cisco 7200 and Cisco 7500 series routers, issue the scheduler allocate 3000 1000 command.
  3. Determine if the router shows symptoms of high CPU utilization at brief and unpredictable intervals. If so, periodically collect the output of the show processes cpu command. This shows if the high CPU utilization is caused by interrupts or by a certain process. Use this UNIX script. Based on the first findings, modify the script to collect data needed for further investigation of the issue.

For more information, refer to Troubleshooting High CPU Utilization on Cisco Routers.

To determine if your problem is related to worms, refer the document High CPU utilization on a router

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