High CPU Utilization Due to Autoconf Process

Platform: - Cisco routers and switches running IOS
Keywords: - : High cpu utilization on Cisco routers using autoconf process, router autoconf
Reference: - cisco.com
Author: - Dinesh Aggarwal

If you are experiencing high CPU utilization (up to 99%) and the show processes cpu command output indicates a large portion of this as the Autoconf process, you are probably hitting a known bug. This problem is filed against software version 12.0(5.4)WC1 and lower.
The problem occurs when you boot a switch which is configured with VLAN 1 interface in the administratively down state without an IP address, and another VLAN interface exists with an IP address that is administratively up . With this configuration, when the switch boots up, it finds that there is no IP address for VLAN 1 and starts the DHCP based auto-configuration. This calls a function in the software which checks for interface VLAN 1 to be up before starting the DHCP, and hence comes up in an infinite loop. This results in the high CPU utilization.
The workaround is to configure the following commands, save the configuration, and reload the switch:

interface VLAN1
no ip address


Note: If you have any other interface VLANs without IP addresses, you will have to follow the same procedure for all of those VLANs.
The following command shows the sample output if the switch is hitting this bug:
Switch#show processes cpu
CPU utilization for five seconds: 99%/7%; one minute: 99%; five minutes: 99%
PID  Runtime(ms)  Invoked  uSecs    5Sec   1Min   5Min TTY Process
   1        4034    538437      7   0.00%  0.00%  0.00%   0 Load Meter
   2           0         1      0   0.00%  0.00%  0.00%   0 IP NAT Ager
   .... output suppressed ....
  62  1888112123 117660129  16047  24.77% 49.89% 51.43%   0 Router Autoconf 
  63       12583      1254  10034   0.00%  0.00%  0.00%   0 SNMP ConfCopyPro
  64          20         9   2222   0.00%  0.00%  0.00%   0 Bridge MIB traps
  66      592259    538607   1099   0.00%  0.00%  0.00%   0 Runtime diags
  67           0         1      0   0.00%  0.00%  0.00%   0 SNMP Timers
  .... output suppressed ....

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