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Knowledge Base

The CPU utilization rate of a city WLAN hang AP consistently keeps high state

Publication Date:  2012-10-08  |   Views:  1098  |   Downloads:  0  |   Author:  SU1000722738  |   Document ID:  EKB1000016743


Issue Description

The CPU utilization rate of a city WLAN hang AP consistently remains for 85% high load.

Alarm Information


Handling Process

1, inquires the AP software version material and related early warning, and at the same time, confirm this version does not have relevant batch problem with research and development, eliminate the causes of BUG version.
2, check AP performance statistics, user number is 0, flow also is not very big, therefore eliminate this phenomenon is due to too many users association or flow problem cause.
<AC01>disp ap-performance-statistic id 529
  AP 529 performance statistic information:
  Memory use rate: 46 %
  Memory average use rate: 46 %
  Cpu use rate: 85 %
  Cpu average use rate: 86 %
  Flash free size: 6044 KB
  Temperature: 47 C
  Online user number: 0
  Up port rate: 0 Mbps
  Up port received frames: 209129
  Up port received right frames: 209129
  Up port received wrong frames: 0
  Up port sent frames: 275235
  Up port received Bytes: 47779777
  Up port sent Bytes: 33671437
  Up port PER: 0 %
  Up port traffic: 26 KB
  Up port traffic(wireless): 0 KB
  Wireless port drop(send) frames: 5385
  Ethernet port drop(receive) frames: 0
  Wireless port receive total Bytes : 4316182057
  Wireless port send total Bytes: 33207846
  Ethernet port send total Bytes: 33671437
  Ethernet port receive total Bytes: 47779777
  Ethernet port drop send frames: 0
  Ethernet port send error frames: 0
  Ethernet port updown counts: 2
3, Looking from process, it is the receive message interrupt occupies CPU high, and found no correlation process stuck and hasn’t been released problem.

Further check statistics, found that have received a large number of wrong packages. May be due to other AP or wireless equipment sent a lot of lip packages, can modify problems AP’s channel to circumvent or to the scene grab lip packages, confirm the interference source and close it.
~ # ifconfig wifi0
wifi0     Link encap:IEEE 80211  HWaddr 54:89:98:48:AC:C0
          RX packets:186842 errors:27278687369 dropped:3814228513 overruns:0 frame:21841861366
          TX packets:95949 errors:5385 dropped:6 overruns:0 carrier:0
          collisions:0 txqueuelen:511
          RX bytes:4316182057 (4.0 GiB)  TX bytes:33207846 (31.6 MiB)
          Interrupt:45 Memory:90011b00f0000000-90011b00f0010000
4, After do corresponding modification and adjustment to AP channel according to the site environment, the CPU utilization returns to normal.

Root Cause

Preliminary judgment according to the situation, there are the following reasons which cause AP CPU utilization high:
1, software version problem causes, appears BUG.
2, AP correlation users too much, flow load is too big causes AP CPU utilization rate rises.
3, Some process of AP stuck but not be released, leading to CPU utilization rate high.
4, nearby interference source is too much, the same frequency interference is strong, causes our company’s AP received too much redundancy message, make the AP CPU processing load increasing.