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High CPU utilization on Access point, loopback interface configured on AP

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Introduction

 

High CPU utilization on Access point, loopback interface configured on AP

 

Core Issue

Users will see the following symptoms in the Wireless network when loopback interfaces are configured on APs

  • When logging onto the AP via telnet, response is slow, and CPU usage is high.
  • One can notice a process consuming the CPU is AiroIAPP Protocol, showing as high cpu usage as compared to other process CPU usage.
  • Sometime the AP dose not respond to pings for a period of around 5 minutes.

 

Resolution

Causes:

  Check for the following if you have high CPU

  • High CPU might be the  result of an IAPP GENINFO storm on the network, which happens if the Access Points (AP) have loopback interfaces configured on them. It is advised that one should remove the loopback interfaces if configured on the AP in order to avoid the IAPP GENINFO storm on the network. This particular issue is also referenced in the release notes, and also found it in the command reference, for information on this refer to Caution statement in the IOS Command Reference Guide.

Caution Access points and bridges do not support the interface loopback command. Configuring a loopback interface might generate an IAPP GENINFO storm on your network.

 

 

  • If  the access point is connected to the switch port make sure the switchport which is connected to the access point is pruned to allow VLANs that the access point is interested .  This reduces the un-necessary trafiic being sent to the access point from the wired network through the switch thereby increasing the access point CPU. Refer Switch Configuration for more information.

Switch Configuration—Catalyst OS

 

In order to configure a switch that runs Catalyst OS to trunk VLANs to an access point, the command syntax is set trunk <module #/port #> on dot1q and set trunk <module #/port #> <vlan list>.

 

An example from to the sample network diagram, is:

 

set trunk 2/1 on dot1q
set trunk 2/1 1,10,30

 

Switch Configuration — IOS Based Catalyst Switches

 

From interface configuration mode, enter these commands, if you want to:

  • Configure the switchport to trunk VLANs to an access point
  • On a Catalyst switch that runs IOS
  • The CatIOS includes but is not limited to: 
    • 6x00
    • 4x00
    • 35x0
    • 295x

 

switchport mode trunk
switchport trunk encapsulation dot1q
switchport nonegotiate
switchport trunk native vlan 1
switchport trunk allowed vlan add 1,10,30

 

Note: IOS based Cisco Aironet wireless equipment does not support Dynamic Trunking Protocol (DTP), so the switch must not try to negotiate it.

 

Switch Configuration—Catalyst 2900XL/3500XL

 

From interface configuration mode, enter these commands, if you want to configure the switchport to trunk VLANs to an access point on a Catalyst 2900XL or 3500XL switch that runs IOS:

 

switchport mode trunk
switchport trunk encapsulation dot1q
switchport trunk native vlan 1
switchport trunk allowed vlan 1,10,30

 

 

  • Based on the additional features configured on the access point amount of CPU relatively increases. For example if access point is configured as WDS as well as serves the wireless clients this happens.

  • Sometimes management stations might flood the access point as a part of of SNMP polling and configuration. Make sure management traffic is in control

As a workaround try to reboot the  access point. If this doesn't help Upgrade the IOS as a last resort.  Backup the configuration before upgrade is done.

To interpret the access point CPU utilization refer  show processes cpu . You can also use Show tech command to check the memory status.

 

Use the show processes EXEC command to display information about the active processes.

 

show processes [cpu]

 

Syntax Description

 

cpu

(Optional) Displays detailed CPU utilization statistics.

 

 

Command Modes

EXEC

 

Command History

 

 

Release

 

Modification

10.0

This command was introduced.

 

 

Examples

The following is sample output from the show processes command:

Router# show processes

 

 

CPU utilization for five seconds: 21%/0%; one minute: 2%; five minutes: 2%

PID QTy           PC Runtime (ms)   Invoked   uSecs     Stacks    TTY  Process

  1 Mwe  2FEA4E         1808            464    3896     1796/3000   0  IP-EIGRP Router

  2 Lst  11682               10236           109   93908     1828/2000   0  Check heaps

  3 Mst  3AE9C                   0           280       0     1768/2000   0  Timers

  4 Lwe  74AD2                   0            12            0     1492/2000   0  ARP Input

  5.ME   912E4                   0             2            0     1892/2000   0  IPC Zone Manager

  6.ME   91264                   0             1            0     1936/2000   0  IPC Realm Manager

  7.ME   91066                   0       30            0     1784/2000   0  IPC Seat Manager

  8.ME  133368                   0             1            0     1928/2000   0  CXBus hot stall

  9.ME  1462EE                   0             1            0     1940/2000   0 Microcode load

10 Msi 127538                   4       76           52     1608/2000   0 Env Mon

11.ME  160CF4                   0             1            0     1932/2000   0 MIP Mailbox

12 Mwe 125D7C                   4           280           14     1588/2000   0 SMT input

13 Lwe AFD0E                    0             1            0     1772/2000   0 Probe Input

14 Mwe AF662                    0             1            0     1784/2000   0 RARP Input

15 Hwe A1F9A                  228           549          415     3240/4000   0 IP Input

16 Msa C86A0                    0           114            0     1864/2000   0 TCP Timer

17 Lwe CA700                    0             1            0     1756/2000   0 TCP Protocols

18.ME  CCE7C                    0             1            0     1940/2000   0 TCP Listener

19 Mwe AC49E                    0             1            0     1592/2000   0 BOOTP Server

20 Mwe 10CD84                  24            77          311     1652/2000   0 CDP Protocol

21 Mwe 27BF82                   0             2            0     1776/2000   0 ATMSIG Input

 

Problem Type

The signal is weak or fluctuating

High CPU load

 

Products

Autonomous Access Points

 

Topology

Wireless client to AP

 

Product OS

IOS

VxWorks

Link Status Meter Test Result

Fair

Poor

Wireless Stages

Authenticated and Associated

 

Reference

 

show processes

Switch Configuration

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